Traffic Signals - tmr.qld.gov.au/media/busind/techstdpubs/Road planning and... · References Style changed as per the other chapters. ... “Manual of Uniform Traffic Control Devices

July 2002 i

Road Planning and Design Manual Chapter 18: Traffic Signals

18Chapter 18

TrafficSignals

ii July 2002

Chapter 18: Traffic Signals Road Planning and Design Manual

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Table of Contents18.1 Introduction 18-1

18.1.1 Purpose 18-118.1.2 Investigation 18-118.1.3 Associated Australian Standards 18-118.1.4 Associated AUSTROADS Guides 18-1

18.2 Warrants 18-118.2.1 General 18-118.2.2 Factors Influencing the Provision of Traffic Signals 18-118.2.3 Mid-Block Pedestrian Crossings 18-2

18.3 Preliminary Design 18-218.3.1 General 18-218.3.2 Physical Layout 18-218.3.3 Traffic Data 18-318.3.4 Bicycles 18-318.3.5 Future Developments 18-3

18.4 Geometric Requirements 18-318.4.1 General 18-318.4.2 Intersection Configuration 18-418.4.3 Traffic Lanes 18-418.4.4 Sight Distance 18-418.4.5 Medians and Islands 18-518.4.6 Left Turn Islands 18-618.4.7 Right Turn Lanes 18-718.4.8 Diamond Turns 18-718.4.9 Ramped Pedestrian Crossings 18-718.4.10 Service Roads 18-718.4.11 Parking 18-818.4.12 Bus Zones 18-8

18.5 Pavement Markings 18-818.5.1 General 18-818.5.2 Stop Lines 18-818.5.3 Pedestrian Crosswalks 18-918.5.4 Longitudinal Lines 18-918.5.5 Turn Lines 18-918.5.6 Pavement Arrows 18-1018.5.7 Painted Islands 18-1018.5.8 Marking for Cyclists 18-10

18.6 Signs 18-1018.6.1 General 18-1018.6.2 Parking 18-1018.6.3 One Way (R2-2), No Entry (R2-4) and No Left/Right Turn (R2-6) 18-1018.6.4 Give Way to Pedestrians (R2-10) 18-1118.6.5 U-Turns Permitted (R2-15) 18-1118.6.6 Left Turn At Any Time With Care (R2-16) 18-1218.6.7 Stop Here on Red Signal (R6-6) 18-1218.6.8 Signals Ahead (W3-3) 18-12

18.7 Signal System and Components 18-1218.7.1 System Purpose 18-1218.7.2 System Process 18-1218.7.3 Components 18-12

18.7.3.1 Vehicular Lanterns 18-1218.7.3.2 Pedestrian Lanterns 18-1218.7.3.3 Associated Equipment 18-1218.7.3.4 Lantern Supports 18-1318.7.3.5 Power Reticulation 18-13

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18.7.3.6 Traffic Signal Controller 18-1318.7.3.7 Detection 18-13

18.7.4 Component Selection 18-1318.8 Phasing 18-14

18.8.1 General 18-1418.8.2 Phasing Elements 18-1418.8.3 Right Turn Movements 18-15

18.8.3.1 Right Turn Ban 18-1518.8.3.2 Right Turn Filter 18-1518.8.3.3 Protected Right Turn 18-1618.8.3.4 Diamond Turn 18-1718.8.3.5 Split Phase 18-17

18.8.4 Left Turn Movements 18-1718.8.4.1 Corner Island 18-1818.8.4.2 No Corner Island 18-1818.8.4.3 Left Turn Bans 18-1818.8.4.4 Arrow Controlled Left Turns 18-18

18.8.5 Late Start 18-1918.8.6 Early Cut-off 18-1918.8.7 Early Start and Green on Yellow 18-1918.8.8 Pedestrian Movements at Intersections 18-1918.8.9 Pedestrian Protection 18-19

18.9 Lanterns 18-2018.9.1 Functions 18-2018.9.2 Assemblies 18-2018.9.3 Left Turn Vehicle Displays 18-21

18.9.3.1 Six Aspect Left Turn Display 18-2118.9.3.2 Five Aspect Left Turn Display 18-2118.9.3.3 Four Aspect Left Turn Display 18-21

18.9.4 Right Turn Vehicle Displays 18-2118.9.4.1 Six Aspect Right Turn Display 18-2118.9.4.2 Five Aspect Right Turn Display 18-2218.9.4.3 Four Aspect Right Turn Display 18-22

18.9.5 Lantern Labelling 18-2218.10 Detection 18-22

18.10.1 General 18-2218.10.2 Detector Types 18-2218.10.3 Vehicle Detection 18-23

18.10.3.1 Characteristics 18-2318.10.3.2 Installation and Location 18-2318.10.3.3 Types of Vehicle Detectors 18-2318.10.3.4 Advance Detection 18-2318.10.3.5 Stop Line Detection 18-2418.10.3.6 Right Turn Detection 18-2418.10.3.7 Counting Detection 18-2418.10.3.8 Queue Detection 18-2418.10.3.9 Violation Detection 18-24

18.10.4 Pedestrian Push Button Detection 18-2418.10.4.1 General 18-2418.10.4.2 Audio Tactile Push Buttons 18-25

18.10.5 Special Detection 18-2518.10.5.1 Emergency Vehicles 18-2518.10.5.2 Rail level Crossings 18-25

18.10.6 Detector Numbering 18-2518.10.7 Detector Logic 18-25

18.11 Controller 18-2618.11.1 General 18-2618.11.2 Location 18-2618.11.3 Full Actuated Control 18-27

18.12 Electrical Design 18-27

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18.12.1 General 18-2718.12.2 Installation 18-2718.12.3 Cables 18-2718.12.4 Vehicle Detector Loop Cables 18-2818.12.5 Data Link Cables 18-2818.12.6 Cable Connection Design 18-2818.12.7 Adaptive Engineering 18-28

18.13 Co-ordination 18-2918.13.1 General 18-2918.13.2 The Case for Co-ordination 18-2918.13.3 Types of Co-ordination 18-29

18.13.3.1 Local Co-ordination 18-3018.13.3.2 Mains FrequencyCo-ordination 18-3018.13.3.3 Centrally Controlled Co-ordination 18-30

18.13.4 Design Factors 18-3018.13.5 Requirements for Signal Design 18-3118.13.6 Timing Criteria 18-32

18.14 Mid-Block Pedestrian Crossings 18-3218.14.1 General 18-3218.14.2 One Stage Crossings 18-3218.14.3 Two Stage (Offset) Crossings 18-32

18.15 Special Situations 18-3318.15.1 Emergency Service Facilities 18-3318.15.2 Adjacent Rail Level Crossings 18-3418.15.3 Early Cut-Off Facilities 18-3418.15.4 Interchange Ramps 18-3518.15.5 Ramp Signal Management 18-36

18.15.5.1 General 18-3618.15.5.2 Ramp Metering 18-3718.15.5.3 Reports 18-37

18.15.6 Roundabout Entrance Metering 18-3818.15.7 Late Start for Large Corner Islands 18-3818.15.8 Temporary Installations 18-39

18.15.8.1 Portable Traffic Signals 18-3918.15.8.2 Temporary Traffic Signals 18-39

18.16 Time Settings 18-4018.16.1 General 18-4018.16.2 Yellow and All-Red Times 18-40

18.16.2.1 Policy for Clearing Interval 18-4018.16.2.2 Calculation of Yellow Times 18-4018.16.2.3 Calculation of All-Red Times 18-40

18.16.3 Other Vehicle Times 18-4118.16.3.1 Late Start Period 18-4118.16.3.2 Minimum Green Period 18-4118.16.3.3 Early Cut-Off Green Period 18-4118.16.3.4 Increment 18-4118.16.3.5 Maximum Variable Initial Green 18-4218.16.3.6 Gap Timer 18-4218.16.3.7 Headway (Space) Timer 18-4218.16.3.8 Waste Timer 18-4218.16.3.9 Maximum Timer 18-43

18.16.4 Pedestrian Times 18-4318.16.4.1 Pedestrian Delay Period 18-4318.16.4.2 Pedestrian Walk Period 18-4318.16.4.3 Pedestrian Clearance Periods 18-43

18.16.5 Presence Timer 18-43References 18-43Relationship to Other Chapters 18-44

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Chapter 18 Amendments - October 2001

Revision Register

Issue/ Reference Description of Revision Authorised DateRev No. Section by

1 First Issue. Steering MayCommittee 2000

2 18.6.3 Modifications to the second paragraph and Steering AugFigures 18.8 and 18.9. Committee 2000

3 Inclusion of new clauses. Steering NovCommittee 2000

4 18.4.5 Figure 18.2 amended to reflect needs of visually impairedusers - ramps oriented to be at right angles to crossing.

18.4.9 Reference to Standard Drawings 1446 and 1447 added.18.5.3 Figure 18.6 modified to cater for visually impaired.18.5.8 New Section - ‘Marking for Cyclists’.18.10.4.1 Push Button access for disabled - changed to 1m above Steering Oct

the surface. Committee 200118.14.3 Minimum width of median changed to 2.0m.18.15.8 Portable traffic signals - Section replaced to reflect the

need to design the use of portable traffic signals.References Style changed as per the other chapters.New Section Relationship to other chapters.

4 18.3.4 New section - Bicycles18.4.4 Modifications to Figure 18.118.4.5 Modifications to Figure 18.2 Steering July18.4.10 Modifications to Figure 18.5 Committee 200218.8.3 Additional text to last paragraph18.11.2 Additional text18.14.3 Additional text and modifications to Figure 18.18

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July 2002 18-1


1818.1 Introduction

18.1.1 Purpose

The purpose of this chapter is to provideguidelines for the provision of a signalisedintersection and requirements for the intersectiondesign.

18.1.2 Investigation

Requests for the installation of traffic signals maycome from many sources. These requests usuallyarise because of an existing problem such as laneblockages, long queues, excessive delays or apoor accident record. In many cases these requestsare well founded, but in others they may arisebecause of an ignorance of basic trafficengineering principles. An investigation shouldalways be carried out to determine whether or nottraffic signals can solve the problem and whetheror not they are the most appropriate solution.

18.1.3 Associated AustralianStandards

This chapter is complementary to AS1742 Part 14“Manual of Uniform Traffic Control Devices -Traffic Signals” and other associated AustralianStandards.

18.1.4 Associated AUSTROADSGuides

AUSTROADS has issued a number ofpublications relevant to signalised intersections,in particular Guide to Traffic Engineering Practice- Part 7: Traffic Signals.

18.2 Warrants

18.2.1 General

This section describes the general warrants for theinstallation of traffic signals. It must beemphasised that these are only a guide. If a sitesatisfies the warrants it does not necessarily meanthat traffic signals are the best solution. All trafficdata should be analysed and alternative treatmentsconsidered to determine the optimum solution.

18.2.2 Factors Influencing theProvision of TrafficSignals

Traffic signals are usually installed at anintersection:

• to provide traffic control at a site with a trafficcapacity or road safety problem;

• to control conflicting movements with hightraffic flows;

• to facilitate access to and from local areas in amajor/minor road system;

• as part of an area wide system of trafficmanagement.

A side effect of signalisation is that the trafficflow on a major road is broken up into platoons.This assists nearby pedestrians to cross the majorroads and allows vehicles in nearby streets tocross or enter the major road.

Factors influencing the provision of traffic signalsinclude:

• traffic flows

• traffic conflicts

• traffic accidents

Chapter 18

Traffic Signals

• pedestrian requirements

• access to major roads

• cost of installation

General warrants for traffic signals are given inthe Main Roads Manual of Uniform TrafficControl Devices Part 14 Section 5.

18.2.3 Mid-Block PedestrianCrossings

The need for a signalised mid-block pedestriancrossing is a function of the probability of apedestrian being able to find a suitable gap invehicular traffic. Finding such a gap depends onthe speed, concentration and flow of vehicles notjust the flow of pedestrians. Therefore factors suchas randomness, number of lanes and upstreaminfluences need to be taken into account as well asthe proportion of children, elderly or handicappedpedestrians and pedestrian desire lines.

Provision for a signalised mid-block pedestriancrossing should consider that the facility mightattract extra pedestrians to the site. Thereforejustification should be based on the potentialpedestrian flow rather than the existing or actualflow.

General warrants for pedestrian traffic signals aregiven in the Main Roads Manual of UniformTraffic Control Devices Part 10 Section 6.4.2.

18.3 Preliminary Design

18.3.1 General

Preliminary design data is used to assess theadequacy of geometric layouts, the location ofsignal equipment, the signal phasing and timesettings. This data can be divided into threecategories:

• physical layout;

• traffic data; and

• planning information regarding futuredevelopments.

Where data is estimated or predicted, the effectsof its accuracy on the design should also beconsidered.

18.3.2 Physical Layout

The following features of the site covering 50mon each approach should be shown on the baseplan (preferably drawn to 1:250 scale):

• relevant property boundaries and buildinglines;

• location of shoulders and kerbs and channelsincluding gully pits, driveway crossings andkerb ramps;

• bicycle lanes;

• edges of medians and islands;

• paved footpaths and driveways;

• parking, bus bays or taxi zones;

• location of all poles and aerial cables;

• location of all service manholes;

• position, type and size of any signs or otherroadside furniture eg bus shelters, guardrail,etc;

• location and nature of road lighting;

• position of any overhead obstructions eg powerlines, shop awning, etc;

• location of trees with diameter of trunk, heightand spread of foliage; and

• location of bridge decks, parapets (incl. height)abutments and relieving slabs.

Additional information required should include:

• vertical geometry of the intersection andapproaches;

• location of any nearby fire station, ambulanceor railway level crossing that may influence thedesign;

• condition of pavement;

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• one way traffic movements;

• photographs taken from each approach to showa clear vision of the intersection and additionalphotographs showing problem utilities orobstructions; and

• any other features that may affect the design.

18.3.3 Traffic Data

Traffic signals should operate over a wide varietyof traffic conditions. While designs are based onpeak traffic conditions, efficient operations atpeak and lower volumes are provided by the useof traffic actuated controllers.

Traffic volumes are expressed in hourly flow ratesincluding turning movements and proportion ofcommercial vehicles. Usually 15 minutessummation intervals are used so the peak flowrates can be identified. Traffic counts may vary byday of the week, weather conditions, school orpublic holidays or other abnormal conditions. Thecircumstances of the count should be adjusted ora recount taken before determining the volumesfor the design.

Counts should identify the pedestrian volumescrossing each vehicle approach and the proportionof children, aged or disadvantaged pedestriansshould be included. These are required to enablespecific features to be designed where necessary.

Bicycle volumes should also be counted bothalong and across each vehicle approach to identifythe need for special features in the design.

Accident data should be obtained to identifyhazard problems for which the signals shouldcater. Accident data for this purpose are bestshown as collision diagrams and it is usual toshow at least three years of data.

18.3.4 Bicycles

The needs of cyclists must be incorporated intothe design. Details of possible treatments arediscussed in Austroads (1999) and in QueenslandTransport’s Bicycle Notes.

18.3.5 Future Developments

During the design of traffic signal installations it isnecessary to consider future developments as thesemay indicate the need for additional featuresand/or equipment eg controller location, ducts andcabling that may become necessary. Whereappropriate these should be included in the design.

18.4 GeometricRequirements

18.4.1 General

This section deals with the aspects of intersectiongeometry that are specific to signalisedintersections. A complete treatment of geometricrequirements is given in Chapter 13 of this Manual.

When designing for traffic signals at anintersection it is important to identify and rectifydeficiencies in the geometric layout to ensure safeand efficient operation and hence obtain themaximum benefit from signalisation.

The design of the intersection should provide for:

• optimum location of traffic signal hardware;

• clearance to traffic signal hardware;

• clearly defined vehicle turning paths;

• adequate sight distances;

• storage requirements;

• minimising the distance between stop lines;

• pedestrian requirements;

• minimising the length of pedestrian crossings;

• medians and left-turn islands (where required);

• exclusive bus or transit lanes;

• auxiliary lanes (where required).

Any changes in the geometry should be inaccordance with Chapter 13 of this Manual butcare should be taken in applying these principles.The combined effect of horizontal and verticalalignment should be considered at all times.

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18.4.2 IntersectionConfiguration

The installation of traffic signals and associatedislands may restrict the movement of largervehicles and it is necessary to choose a suitable‘design vehicle’. The turning path characteristicsof the ‘design vehicle’ are used to ensure thatpavement widths, alignments, kerb locations androadside furniture positions are suitable.

Because of these requirements larger turning radiimay be considered. The following problems areassociated with the use of larger radii especiallyfor left turning movements:

• hazard to pedestrians by increased turningspeed;

• delays because of increased clearance times asthe stop lines are located further from theintersection;

• longer pedestrian crossing distances ordeviations from their direct route;

• difficulty of achieving optimum lanternpositioning and aiming.

Use of smaller radii may require large vehicles toencroach on other traffic lanes but this may beacceptable if occurring infrequently.

Refer to Chapter 13 dor details of geometricdesign.

18.4.3 Traffic Lanes

The number of traffic lanes to be provided on aparticular approach depends on the traffic flow,available width and scope for future widening.

To increase the capacity of a particularintersection approach the number of lanes on thatapproach or on other approaches may need to beincreased. This can be achieved by either reducingthe width of existing lanes or by widening theapproach and departure carriageways andproviding appropriate tapers to allow properusage of the lanes.

Through lanes across an intersection should be

aligned to achieve clear definition of vehiclepaths. When it is desired to store vehicles inseparate turning lanes adjacent to through trafficlanes it is important to ensure that adequatestorage length is provided. Where adequatestorage length cannot be provided the signalphasing may need to be modified.

18.4.4 Sight Distance

Sight distance requirements for a signalisedintersection should be in accordance with Chapter13. The combined effect of horizontal and verticalalignment on sight lines and stopping distancesmust be considered at all times. In additionstopping sight distance (refer Figure 18.1) shouldbe the minimum available to:

• provide clear sight of primary, overheadprimary or dual primary lanterns as applicable;

• the rear end of a stored vehicle or stationaryqueue.

Figure 18.1 Stopping Sight Distance

If stopping sight distance to primary or dualprimary lanterns is inadequate then overheadprimary lanterns will be required if regrading isnot carried out.

If stopping sight distance to the rear of a storedvehicle or stationary queue is insufficient theprobability of a rear end collision is high. Ifvehicle B is a through vehicle there is no simplesolution to the problem of inadequate stoppingsight distance other than regrading. If vehicle B iswaiting to make a turn then possible solutions areto:

• provide an exclusive turn bay;

• ban the turn;

• split the approach phasing;

• regrade.

<S.S.D.

BA

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If the road alignment does not provide sufficientsight distance and the existing geometry cannot beadjusted, provision of advance warning signs(W3-3) or advance warning signals eg flashingyellow lights will be necessary.

18.4.5 Medians and Islands

The following criteria should be observed whendesigning median islands at signalisedintersections:

• a minimum clearance from face of kerb to thesignal lantern target board of 0.5m is desirablerefer (Table 18.1);

Table 18.1 Minimum Widths of Raised Medians*

Situation Desirable Absolute(m) (m)

No posts 1.2 0.9Post with single 2.4 1.2200mm lanternsPost with dual 2.4 1.5200mm lanternsTwo-stage mid-block 4.0 4.0pedestrian crossing

* Residual median at the signals.

• where pedestrians are likely to accumulate onmedians or islands the width should be aminimum of 1.5m to 2.0m (refer AS1742);

• if a protected right turn lane is provided, theresidual median width should satisfy the abovetwo dot points;

• the use of wide medians reduces capacitybecause of increased clearance times. Widemedians may cause the problem of interlockingopposing right turn vehicles and thereforeshould be avoided;

• the ends of medians and islands should be setback a minimum 0.6m behind the prolongationof the kerb lines or full shoulder width unless apedestrian crossing is provided;

• when a pedestrian crossing is provided themedian should preferably terminate at the

crossing unless a gap in the median as wide asthe crossing is provided and the mediancontinued for at least 2m beyond the crossing(refer Figure 18.2).

Figure 18.2 Treatment at Pedestrian Crossings

While the minimum width of median is stated as0.9m (no posts) in Table 18.1, lesser widths ofpainted median may be used. The use of back-to-back median kerb is not recommended as it is:

• not readily observable by approaching driversparticularly in bad weather;

• a hazard for errant vehicles straddling it;

• not wide enough to provide adequate refuge forpedestrians.

Where a two-stage signalised pedestrian crossingis used, the median must be a minimum of 2m(2.5m to 4.0m desirable) wide to allow forpedestrian storage.

Median islands for minor channelisation shouldbe at least 10m long to ensure adequateconspicuity. If a signal post is provided it shouldbe at least 1.2m wide.

Painted medians or islands may be used wherethere is not sufficient carriageway to construct a

PreferredTreatment

AlternativeTreatment

2.0mminimum

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kerbed median or island or where it is desirable topermit vehicles to cross the median.

Traffic signal posts should always be locatedbehind raised kerbing and must not be placed inthe painted areas.

18.4.6 Left Turn Islands

Left turn islands for slip lanes may be used asshown in Figure 18.3 to:

• reduce the distance between stop lines;

• reduce the length of pedestrian crossings;

• enable the free flow of left turn vehicles wherethis would benefit capacity withoutendangering pedestrians.

Left turn islands should be designed toaccommodate traffic signal equipment, storage ofpedestrians and the ends of any stop lines andpedestrian crossings including tactile indicators.Providing for all of the needs of users, togetherwith the physical space needed to accommodatethe equipment requires an island of sufficient sizeto avoid congestion and clutter. A minimum sizeof 25m² should be provided (see Chapter 13).

To minimise the consequences of a possiblepedestrian/vehicle conflict, kerb radii in excess of20m should be avoided, keeping design speeds toapproximately 30km/h or less. The preferredtreatment is to reduce the left turn speed byredesigning the kerb line as shown in Figure18.4(b). The side street phase pedestrianmovement may be protected if required. (See alsoChapter 13, Sections 13.8.6, 13.8.7, 13.8.8.)

Figure 18.3 Left Turn Island Treatments

Figure 18.4 Reduction of Left Turn Speed

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18.4.7 Right Turn Lanes

Where through and right turn vehicles share a lanethe following may occur:

• hazardous situations created by a right turningvehicle stationary in a through lane;

• blocking a through lane increasing intersectiondelays;

• inefficient use of any right turn phase.

Exclusive right turn lanes are therefore desirableon all intersection approaches where trafficvolumes are sufficiently high (see Chapter 13,Figure 13.21). A correctly designed right turn lanewill provide a deceleration length and a storagelength long enough to accommodate themaximum expected queue of right turn vehicles.If the deceleration length cannot be achieved (as isoften the case in urban areas) the lane should be atleast long enough to accommodate the stored rightturn vehicles so they do not overflow and blockthe adjacent through lane. They should also belong enough to allow the right turn vehicles toenter the right turn lane without being blocked bythe queue of vehicles in the adjacent through lane.

The calculation of the expected queue lengths canbe carried out by computer analysis eg SIDRA(Simulated Intersection Design Research Aid).(Refer also to Chapter 13, Appendix A13.3.1).

18.4.8 Diamond Turns

Designs should provide sufficient clearance fordiamond turns ie opposing right turns operatingconcurrently and be in accordance with Chapter13, Section 13.8.4.8. Where there is insufficientwidth for a diamond turn either one of the turnsmust be banned or the phasing altered so that theright turns operate during different parts of thecycle eg split approach phasing.

18.4.9 Ramped PedestrianCrossings

Ramped pedestrian crossings should be providedat all pedestrian crossings whether signalised or

not. The number and position of ramps aredetermined by considering the general movementof pedestrians, the location of pedestrian crossingsand any obstacles such as traffic signal posts andutilities. Wherever practical ramps should belocated downstream of adjacent gully pits.

Ramps should be installed so that they guidepedestrians (particularly the visuallyhandicapped) across the road by the most directroute. Detailed requirements are shown inStandard Drawings 1446 and 1447.

See Chapter 7 for details of this type of crossing(kerb types 18, 19, 20, 21).

18.4.10 Service Roads

Service roads should not generally be carriedthrough signalised intersections because theycause:

• reduction in safety due to the greater number ofconflict points, the larger intersection conflictarea and the difficulty for the right turningmotorist to select appropriately sized gaps inopposing traffic on two carriageways;

• reduction in intersection capacity because ofincreased pedestrian and vehicle clearancetimes.

Therefore where service roads are providedproblems can be minimised by terminating theservice road or by carrying it around the corner asa left turn movement only. See Figure 18.5 fortypical examples.

Alternatively, if space is available, the serviceroad can be “bulbed” to intersect the cross road ata distance from the intersection sufficient to forma separate intersection. This distance will belonger than the expected queue at the intersectionor a minimum of 20 m (allows a semi trailer to doa U-turn between inside lanes).

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Figure 18.5 Typical Service Road Treatments

18.4.11 Parking

Vehicles parked near an intersection can cause thefollowing:

• reduction in the numbers of effective lanes onan approach ;

• reduction in the numbers of effective departurelanes;

• misleading activations of the traffic detectors;

• obstruction of signal displays and other controldevices;

• reduced sight distances for vehicle orpedestrian traffic;

• delays as vehicles manoeuvre into parkingspaces.

Where statutory restrictions are not adequateparking prohibitions and restrictions are necessaryto reduce these difficulties.

18.4.12 Bus Zones

The effect of bus bays or zones close to anintersection is similar to that of short term parking.Bus stops on the approaches cause detectiondifficulties if placed between the loops and the stopbar and when designing bus priority schemes. Busstops on the departure sides can cause platoons ofvehicles to queue through the intersection and theuse of bus bays should be considered.

18.5 Pavement Markings

18.5.1 General

This section discusses some of the pavementmarking requirements specific to signalisedintersections. General requirements for pavementmarkings are given in the Main Roads Manual ofUniform Traffic Control Devices Part 2 Section 4.

18.5.2 Stop Lines

Stop lines should be located:

• so as to minimise intergreen times andclearance times;

• not less than 3m from conflicting vehiclemovements;

• clear of the swept path of vehicles turning fromother approaches;

• a minimum of 1.0m from parallel pedestriancrossings at intersections;

• a minimum of 3m from signalised mid-blockpedestrian crossings;

• at a desirable 10m in advance of the starting(secondary) lantern for that approach except formid block pedestrian crossings; and

• at a maximum skew of 70 degrees to thedirection of travel (over 70°, stop line may bestepped).

TREATMENT A

TREATMENT B

TREATMENT C

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18.5.3 Pedestrian Crosswalks

The pedestrian crosswalk widths should be atleast 2m wide. This should be increased whenthere are heavy pedestrian volumes.

Pedestrian crossings should be located:

• as near as possible to the desire lines ofpedestrians;

• as near as possible to and no greater than 20degrees from the shortest path across thecarriageway to minimise clearance times;

• as close to, but at least 0.6m clear of, parallelvehicle movements.

Where two pedestrian crossings meet theintersection point of the outside edges should beno more than 1m from the face of the kerb (Figure18.6). This is to minimise conflicts by pedestriansin separate phases and to deter pedestrians fromwaiting on the road pavement.

Figure 18.6 Intersection of Pedestrian Crossings

Where a pedestrian crossing is provided to a leftturn island the crossing ends at the kerb not at thepainted chevron. This is to discourage pedestriansfrom standing on the road pavement (Figure18.7).

Figure 18.7 Pedestrian Crossings at Left TurnIslands

18.5.4 Longitudinal Lines

To control overtaking in the vicinity of theintersection and the position from which rightturns are made, a median island, barrier lines or asingle unbroken line may be used. The length ofbarrier line should be 27m minimum from thestop line and further extended if required.Requirements for kerbside parking and access toproperty entrances adjacent to the barrier lineshould be considered.

Broken lane lines should be provided wherepossible for at least 51m on the approach and 27mon the depart side of an intersection. Wherenecessary to improve lane discipline lane linesmay be marked as unbroken lines.

18.5.5 Turn Lines

Turn lines may be used to provide delineation toguide two or more streams of traffic which turnsimultaneously in the same direction or provideguidance through intersections with unusualgeometry, skewed approaches or lanes not alignedacross the intersection.

Turn lines should not be carried throughpedestrian crosswalks.

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18.5.6 Pavement Arrows

Pavement arrows should be used:

• in auxiliary lanes (left or right) to avoidinadvertent use by through vehicles;

• to allow movements that would not otherwisebe allowed under traffic regulations;

• to prohibit movements that would otherwise beallowed under traffic regulations.

Pavement arrows should not be used to reinforcelane usage that is regulated by traffic regulations.If drivers are breaking the law relating to laneusage it may indicate that the existing lanedistribution is inappropriate and may need to bechanged.

A minimum of three arrows in any lane should beprovided.

18.5.7 Painted Islands

Where painted islands are used at signalisedintersections traffic signal hardware must not bemounted on them.

18.5.8 Marking for Cyclists

The special needs of cyclists at intersections canbe accommodated in a range of ways, dependingon the circumstances involved. Details of themarking systems for cyclists at intersections areprovided in Austroads (1999), QueenslandTransport’s Bicycle Notes and Part 14 of theMUTCD.

18.6 Signs

18.6.1 General

This section refers to signs that are uniquelyassociated with traffic signals. Generalrequirements for signs are given in the MainRoads Manual of Uniform Traffic ControlDevices.

18.6.2 Parking

Signs controlling or prohibiting parking orstanding are used extensively in the vicinity ofsignalised intersections to improve capacity andto reinforce statutory no standing requirementsassociated with traffic signals.

18.6.3 One Way (R2-2), NoEntry (R2-4) and NoLeft/Right Turn (R2-6)

Traffic signals at the intersection of one or moreone-way streets need to be signposted to eliminatethe possibility of confusion to motorists.

When a right turn movement is banned to denywrong-way entry to a one-way street a No RightTurn sign should be placed on the post carryingthe primary lantern and a One Way sign on thepost carrying the tertiary lantern (Figure 18.8).

Figure 18.8 Left Turn Movement

When a left turn movement is banned to denywrong-way entry to a one-way street a No LeftTurn sign should be placed on the post carrying thedual primary, overhead primary and primarylantern and a One Way sign on the post carryingthe secondary lantern (Figure 18.9).

R2-2(L)

ONE

WAY

ONE WAY

R2-6(R)

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Figure 18.9 Right Turn Movement

When a through movement is banned to denywrong-way entry to a one-way street a No Entrysign should be placed on the posts carrying thesecondary and tertiary lanterns (Figure 18.10).

Figure 18.10 Through Movement

18.6.4 Give Way to Pedestrians(R2-10)

This sign is only used at signalised intersectionswhere there is a need to remind drivers of right orleft turning vehicles that although they are stillunder the control of the intersection signals theymust give way to pedestrians.

The sign should not be used except in specialcircumstances because indiscriminate use wouldreduce the effectiveness of the general regulationapplying to signalised intersections.

18.6.5 U-Turns Permitted (R2-15)

U-turns are prohibited by regulation at allintersections controlled by traffic signals.Therefore signs prohibiting U-turns should not beinstalled.

Where it is considered desirable and safe to relaxthis rule the U-Turn Permitted sign is used. As ageneral rule the sign should only be used onintersection approaches with medians andpreferably with right turn auxiliary lanes.

U-turns should only be permitted where:

• geometry is sufficient to allow the U-turn to bemade in one manoeuvre by vehicles of the typelikely to U-turn;

ONE WAY

R2-4

NO

ENTRY

R2-4

NO

ENTRY

R2-2(R)

ONE

WAY

R2-6(L)

PRIORITY 1

ONE WAY ONE WAY

PRIORITY 2

PRIORITY 3

R2-2(R)

ONE

WAY

R2-6(L)

ONE WAY ONE WAY

ONE WAY ONE WAY

R2-2(R)

ONE

WAY

R2-6(L)

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• there are no more than two lanes of opposingthrough traffic;

• there is adequate visibility of approachingvehicles;

• there would be no danger to pedestrians.

18.6.6 Left Turn At Any TimeWith Care (R2-16)

The sign Left Turn At Any Time With Care shouldonly be used at an intersection controlled bytraffic signals where there is a slip lane for the leftturn movement not required to comply with thetraffic signals and falls clearly within theboundary of the intersection.

It should be mounted on the left hand side at thebeginning of or within the slip lane but may belocated on the right hand side so that it faces onlythe traffic approaching and using the slip lane.

18.6.7 Stop Here on Red Signal(R6-6)

This sign is not intended for routine use atsignalised intersections. Its use is generallylimited to situations where signals might beunexpected such as fire station or ambulancesignals which are only in use in an emergency.

18.6.8 Signals Ahead (W3-3)

This sign is required where signals are located inan unexpected position eg restricted visibility onthe approach to lanterns or end of queue, ortemporary signals.

Where there is a high risk of rear-end collisionswith vehicles stopped against a red signal the useof Advance Warning Signals incorporating theSignals Ahead sign should be considered. Adevice of this type should be located at not lessthan the stopping distance in advance of theprobable end of queue.

18.7 Signal System andComponents

18.7.1 System Purpose

Signal control is provided to:

• reduce traffic conflicts and delays;

• share times between conflicting movements;

• reduce accidents.

18.7.2 System Process

Demands for traffic movements are identifiedthrough vehicle detectors, pedestrian push buttonsand externally supplied data from area controlmasters. The signal system transforms trafficdemands in a manner determined by the controlleralgorithms and operational settings into asequence of signal displays.

18.7.3 Components

18.7.3.1 Vehicular Lanterns

These lanterns convey the control signals tovehicular traffic. They include 200mm and300mm diameter red, yellow and green aspectsand may have arrow masks or other qualifyingsymbols.

18.7.3.2 Pedestrian Lanterns

These lanterns are provided for the control ofpedestrians. Red and green symbolic displays areused.

18.7.3.3 Associated Equipment

Visors are used to minimise sunphantom effectsand to reduce the possibility of a signal being seenby traffic for which it is not intended.

Louvres may be used to minimise sunphantomeffects when oriented horizontally or to reduce thepossibility of a signal being seen by traffic forwhich it is not intended. As louvres constrict light

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distribution their use should be restricted toessential locations.

Target Boards surround the signal lantern inorder to improve the visibility of the signal. Blacktarget boards provide the best signal conspicuity.

Symbolic displays (masks) such as arrows can beused to mask signal aspects. These displays areused to dedicate the aspect for a particularmovement or vehicle type.

18.7.3.4 Lantern Supports

Posts, poles, brackets and straps are used tosupport the signal lanterns at the required height.Posts may be up to 5.1m in height. Joint use polesor mast arms may be up to 12m in height with upto 6.5m outreach. Joint use poles are used toreduce the number of poles at a particular site.Typical examples are illustrated in StandardDrawing 1420.

18.7.3.5 Power Reticulation

The supply of power throughout the signalinstallation is made via traffic signal cable that islaid underground in ducting. Changes of directionin the ducting are made at junction pits. Junctionpits are provided adjacent to the controller cabinetand each signal post or pole. Junction pits andterminal assemblies provide for the connection ofthe cable to the signal equipment.

The signal cable provides 240 volt (nominal)50Hz power to the signal lanterns and other trafficdemands and 32 volt circuits for the pedestrianpush buttons. This is a low voltage installationand must be installed to the requirements ofStandard Drawing 1149 and AS/NZS 3000 -Wiring Rules.

18.7.3.6 Traffic Signal Controller

The traffic signal controller regulates thesequence and duration of aspects and intervals.

Main features of this equipment include:

• circuit breakers for the signal lanterns; controlsfor safe display of lanterns by interlocking or

solid state switching; monitoring by current andvoltage feedback to green and red aspects;

• provision for display of minimum greenperiods and safe clearance periods betweenconflicting movements;

• storage of detector and push button informationto determine the sequence and duration ofgreen displays;

• facilities for traffic personnel to monitor oralter its operation;

• communication and other facilities to allowcontrol by a remote master controller orcomputer.

18.7.3.7 Detection

The most common form of vehicle detector is theinductive loop sensor. Several turns of wire (seeStandard Drawing 1424) are placed in a slot cut inthe road pavement. The wire is connected via afeed cable to a detector sensor unit mounted in thecontroller cabinet. A vehicle (ie a large mass ofmetal) presence or movement over a loop reducesthe loop inductance and causes a detector output.This output is the closure of a relay contact or theequivalent operation of a semiconductor.

Pedestrian demands are recorded when apedestrian presses a push button mounted on theside of the signal post or pole.

Detection of bicycles and light motor cycles isdifficult but may be achieved by using specialloop designs and sensitive detectors. Refer toAustroads (1999), Part 5.4.1.

Priority vehicles may also be detected if specialdetector systems are used.

18.7.4 Component Selection

The selection of the components to be used for asignal installation will be determined by the signaldesign. Consideration should also be given topractical restrictions such as availability ofcomponents, maintenance requirements, stockholdings, price and standardisation of installation.

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Some modifications to design may be required inorder to achieve overall economic efficiency forthe supply, installation and maintenance of thesystem.

18.8 Phasing

18.8.1 General

The choice of phasing for a particular intersectiondepends primarily on the flows of vehicles andpedestrians for each movement. Phasing can alsodepend on geometry. Design strategies should beto:

• minimise the number of phases to make bestuse of the available time;

• minimise the cycle time;

• run as many compatible movements as possibleduring each phase;

• restrict each phase to non-conflictingmovements;

• allow each movement to run in as many phasesas possible.

Design objectives are:

• promote safety, efficiency, consistency andsimplicity;

• optimise capacity and reliability;

• minimise operation costs and driver frustration.

In practice it may not be possible to achieve allthese objectives simultaneously so a compromisemay be necessary. Safety is the foremostconsideration when determining compromise.

A signal group is a set of lanterns that share thesame colour sequence within each phase and foreach phase sequence. A signal group may controlone movement or a number of movements.

This section provides guidelines to the selectionof phasing and discusses techniques for ensuringthat the signal group display sequences are safeand efficient.

18.8.2 Phasing Elements

The simplest form of phasing at an intersection istwo phases which allocates Phase A to the mainstreet and Phase B to the cross street as shown inFigure 18.11.

This phasing leaves four crossing conflicts(between right turn vehicles and throughvehicles), four merge conflicts (between right turnvehicles and left turn vehicles) and eightvehicle/pedestrian conflicts (between left/rightturn vehicles and pedestrians.

Nevertheless this phasing will usually work quiteadequately for a site with geometry and sightdistance which meets the required designstandards, no record of severe accidents and lowvehicle and pedestrian flows because the priorityfor each conflict is determined by the trafficregulations.

Figure 18.11 Two Phase Design

As the potential safety and efficiency of anintersection declines due to poorer geometry,inadequate sight distance, reduced capacity orincreased vehicle or pedestrian flows it becomesnecessary to increase the number of phases anduse more complex phasing by using additionalsignal groups to control certain movements.

Phases for protecting right turns are the mostcommonly added phases. The basic sequencesthat accommodate right turn movements include:

A phase

B phase

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• Protected Right Turn. This is a right turningmovement in which only one approach isprotected and moves on the arrow indication. Ifpreceding the opposing through movement it istermed a ‘leading right turn’ and if following a‘lagging right turn’.

• Diamond Turn. This is a right turningmovement where the opposing right turns movesimultaneously in a phase of their own.

• Diamond Overlap Turn. In this operation theopposing right turns start simultaneously.When one terminates the through movement inthe same direction as the extending rightmovement is started. When the extending rightturn is terminated the other through movementis started. It is usually used in preference to adiamond turn.

• Lead-Lag Turn. This phasing is thecombination of a protected leading right turn inone direction followed by the throughmovements then by a lagging right turn in theopposing direction. It is usually used in systemsto provide a wider two-way through band.

• Split Phase. This phase is where themovements of opposing traffic flow in totallyseparate phases. The right turn and associatedthrough movements flow at the same timewhilst all opposing movements are stopped.

Although there are no limitations to the number ofphases that can be utilised they should be held toa minimum. Movements that run in more than onephase should preferably be allowed to overlap toreduce delays and improve safety. However, thereare situations where this is not possible becauseother more dangerous conflicts would result. Inthis case it is necessary to stop the relevantmovements and restart them following a suitabledelay.

18.8.3 Right Turn Movements

There is no formal warrant or guideline availableto determine whether or not a protected right turnphase is required. It will depend upon siteconditions, traffic flows and signal timings. As ageneral rule it should be considered when two or

more vehicles turn right each cycle.

The protected phase is required if motoristsattempting to make a right turn have insufficientopportunities to filter during the through phaseand intergreen period and generally when threethrough lanes are being crossed. This results in theright turn movement being delayed or motoriststaking unnecessary risks.

For existing intersections the need for a protectedright turn phase can usually be determined byobserving the operation of the intersection. If theright turn queue regularly does not clear in a cycleand the intersection is operating at a relativelyhigh cycle time then a protected right turn phase isneeded. At signals operating on short cycle timesextending the through phase green time willincrease the opportunity for vehicles to turn right.This can be accomplished by utilising presenceloops to detect vehicles waiting to turn right andextending the through phase with this detection.

Where traffic conditions are changing or a newintersection is being designed, it is not possible toobserve traffic operations. The need for aprotected right turn phase must be based on trafficvolumes. In general a protected phase will berequired if there are more than 200 vehicles/hourturning against more than 600 vehicles/hour. Aprotected right turn phase would not be requiredwhere the right turn volumes are less than 60vehicles/hour depending on the opposing volumeand alternative access arrangements.

18.8.3.1 Right Turn Ban

Banning the right turn should be avoided unlessthe right turn flows are low and a suitablealternative route is available.

18.8.3.2 Right Turn Filter

A right turn filter is where right turn vehiclesselect gaps in the opposing vehicle flow. The flowrate of a filter right turn is affected by:

• the rate of the opposing flow;

• the speed of the opposing flow;

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• the number of lanes (or width of the road) thatthe right turn vehicles must cross;

• the length of phase during which the filter maytake place.

Often one or two vehicles will be able to filterduring the intergreen period. Any right turnvehicle that has crossed the stop line during thegreen interval may legally complete the turnduring the intergreen.

A filter right turn should not be permitted onapproaches where:

• sight distance is insufficient to filter safely;

• there is more than one right turn lane;

• it is possible for a yellow signal to be displayedto the right turn vehicle when the opposingapproach has a green signal, eg the opposingapproach has a lagging right turn or theapproach with the right turn has an early cut-off;

• the 85th percentile speed of the opposing trafficis greater than 70km/h and the right turn has tofilter across more than two lanes;

• there is an adverse traffic accident historyinvolving filtering right turn vehicles;

• the opposing approach is four lanes or morewide.

18.8.3.3 Protected Right Turn

A right turn phase can be provided as the onlymeans by which vehicles are permitted to turnright or it can be provided in addition to a filterright turn permitted in another phase.

A right turn phase can operate as a leading rightturn or a lagging right turn. Both the leading andlagging right turns can operate with or without theright turn operating as a filter movement.

A leading right turn occurs when the right turnphase precedes the phase in which the opposingthrough movement runs as shown in Figure 18.12.

Figure 18.12 Leading Right Turns

A lagging right turn occurs when the right turnphase follows the phase in which the opposingthrough movement runs as shown in Figure 18.13.This phasing cannot be used at cross roads wherethe other right turn filters.

Figure 18.13 Lagging Right Turn

When a right turn movement operates as a phaseand filter turn:

• the lagging right turn sequence is normallyused when the opposing right turn filter can bebanned and is preferred at T junctions;

• the leading right turn sequence is normally usedwhen the opposing right turn filter is light andcannot be banned;

• specific signal groups are required undercertain conditions for safety reasons.

Right Turn filtering inthrough phase

Right Turn not filteringin through phase

Right Turn held onred then filtering

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Figure 18.14 Diamond Turn

Figure 18.15 Diamond Overlap Phasing

18.8.3.4 Diamond Turn

When it is necessary to signalise opposing rightturns and exclusive right turn lanes are available itis possible to allow both right turns to runsimultaneously while the through movements arestopped. This is called a diamond turn and isshown in Figure 18.14.

This phasing is inefficient and is notrecommended. It should only be considered whenboth right turn flows are the same under all flowconditions. It is more efficient to use a diamondoverlap turn.

Diamond Overlap Turn

Diamond overlap phasing is the combination of adiamond turn with alternative overlaps for oneintersecting street as shown in Figure 18.15. Thisphasing is more flexible and efficient thandiamond turn phasing because it can cater for

widely varying demands. It is possible to have afilter option in A phase on either or both right turnmovements.

Where diamond overlap phasing is required onboth intersecting streets a double diamond overlapcan be used.

18.8.3.5 Split Phase

Split phase operation as shown in Figure 18.16 isusually only used on side street approaches. It isused where appropriate if both right turnmovements require to be protected or where aparticularly heavy right turn movement isopposed by a very light movement (the right turnmovement may fail to give way to randomarrivals on the through movement).

If a pedestrian movement is allowed to runconcurrently with each of the split approach phasesthen the combined clearance times may exceed thecycle time required by vehicle actuation alone.Therefore when using split phasing one of thepedestrian crossings should be sacrificed.

Figure 18.16 Split Phasing

18.8.4 Left Turn Movements

Left turns can be designed in two ways, with orwithout a corner island. The lane created by usinga corner island is called a slip lane. In most casesonly one slip lane is required but more lanes canbe provided if warranted by traffic flows.

The approach left turn lanes may be shared orexclusive. A shared left turn lane is one wherethrough vehicles use the same lane as the left turnvehicles.

An exclusive lane (dedicated lane) is used solelyby left turn vehicles.

A Phase B Phase C Phase


C1 Phase C2 Phase


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Signal control of left turns can be complexdepending on whether the turn is from a sharedlane, an exclusive lane, conflicts with a signal-controlled pedestrian crossing or overlaps fromone phase to another.

Depending on site conditions and constraints aleft turn movement can be permitted to operate in:

• one phase;

• separate phases (overlapping/non overlapping);

• all phases (exclusive protected depart lane - leftturn on red is not permitted in Queensland).

18.8.4.1 Corner Island

If a corner island is provided, ie there is a sliplane, the left turn movement can be allowed toturn:

• left at any time it is safe to do so by providinga Turn Left At Any Time With Care sign(G9-14);

• at any time into an exclusive departure lane;

• when a left turn green aspect is displayed.

The first two options are not controlled by signals.

18.8.4.2 No Corner Island

If a corner island is not provided, ie there is no sliplane, the left turn movement can be:

• banned;

• allowed to run concurrently with other vehicleson the same approach by displaying a full greenaspect;

• allowed to run independently of other vehicleson the same approach by displaying a left turngreen arrow.

18.8.4.3 Left Turn Bans

Banning a left turn is very rare and should beavoided unless the left turn geometry is sorestrictive that vehicles cannot safely negotiatethe turn.

18.8.4.4 Arrow Controlled LeftTurns

Left turns can be controlled for one phaseoperation by either a three aspect lantern or fouraspect lantern (three roundels plus a green arrow).For more than one phase operation left turns canbe controlled by a three plus two aspect lanterns(three roundels plus green and yellow arrows) ortwo three aspect lanterns (three roundels plus red,yellow and green arrows).

Left turn vehicles can normally be catered forduring the same phase as the through vehicles onthe same approach. However it is often beneficialto increase the left turn capacity by allowing theleft turns to run complementary to a right turnphase as shown in Figure 18.17. At a T junction itmay be included to run complementary to the sidestreet movement.

Figure 18.17 Left Turn Green Arrow

There are situations where providing a left turngreen arrow does not improve capacity. If the leftturn flow is low and the lane is shared with arelatively heavy movement, few vehicles will beable to turn left because they will be blocked bythe through vehicles; therefore the left turn arrowsshould be omitted. A similar situation occurs withshared lanes when a pedestrian movement delaysthe left turn blocking the passage of the throughmovement.

The suitability of providing the left turn duringthe corresponding right turn phase should betested by computer analysis.

Left turn arrows should only be used whenvehicles can turn without conflict with othervehicles or pedestrians.

Left turn arrows can also be used to provide forpedestrian protection. The left turn is stopped

ThroughRoad

Side Road

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using a left turn yellow arrow followed by a leftturn red arrow which is held for a predeterminedperiod.

18.8.5 Late Start

Uses for a late start interval are:

• to delay the introduction of the throughmovement in a trailing right turn when therewas an opposing right turn filter in the previousphase;

• to delay the introduction of a right turn filterwhen it was controlled by a right turn greenarrow in the previous phase;

• to delay the introduction of a left turn greenarrow when the left turn movement has beenheld during the intergreen because it is in ashared lane which was controlled by a fullgreen in the previous phase;

• to delay the introduction of a left turn greenarrow when the left turn movement has beenheld during the intergreen because of anopposing right turn filter in the previous phase.

18.8.6 Early Cut-off

The early cut-off interval is used to terminate onemovement before another within the same phase.A typical application is at intersections withdouble stop lines such as staggered T junctions.

18.8.7 Early Start and Green onYellow

Early start and green on yellow allow somemovements to commence earlier than otherswithin the same phase. This is usually associatedwith the early cut-off interval of another phase.

18.8.8 Pedestrian Movementsat Intersections

When a signalised pedestrian crossing is providedat a signalised intersection, the pedestrian

movement normally runs in association with theparallel vehicle movement. When this occurs caremust be taken to avoid unsafe sequences. Forexample if a pedestrian demand is received afterthe parallel vehicle green aspect is displayed, itmay be unsafe to introduce the pedestrianmovement due to the conflict with the left or rightturning traffic.

To avoid such conflicts and where there is nodemand for another phase, the pedestrian pushbutton actuation shall first 'call away' to anotherphase and stop the parallel traffic for a minimumperiod. The pedestrian and vehicle green aspectsare then introduced simultaneously.

Where there are no conflicts between vehicle andpedestrian movements (one way streets or cornerislands), the pedestrian movement may be re-introduced or late introduced while the parallelvehicle signal group is green.

When a signalised pedestrian crossing is parallelto an overlap vehicle movement, the pedestrianmovement should also be capable of overlapping.In this way the first phase of the overlap does notneed to be prolonged in order to terminate thewalk and clearance intervals.

Exclusive (scramble) pedestrian phases eliminateall vehicle/pedestrian conflicts and provide thehighest level of safety for pedestrians but theyhave several disadvantages. Pedestrian clearancetimes need to be longer, reduced vehicle greentimes may lead to driver frustration, particularly inoff peaks when drivers are unable to perceive whythey are delayed for the sake of perhaps a singlepedestrian crossing an approach parallel to theirmovement and oversaturation in peak periods.

Despite the disadvantages, exclusive pedestrianphases have been found to be beneficial at certainsites in central business districts and busyshopping centres where heavy, consistentpedestrian movements would otherwise causeexcessive conflicts with vehicular traffic.

18.8.9 Pedestrian Protection

Protection for pedestrians should be consideredwhenever pedestrians are placed at an

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unnecessarily high risk by the introduction of thepedestrian movement. This includes poorlylocated crossings, sites with poor visibility, highspeed turns, two lane left turns and crossings usedby pedestrians with special needs such aschildren, the aged and the handicapped.

The degree of protection depends on thecircumstances and may be:

• no protection;

• timed protection for part of the walk interval;

• timed protection for all of the walk interval;

• full protection for all of the walk and clearanceintervals.

As a guide, pedestrian protection is usuallyunnecessary when all of the following conditionsare met:

• the crossing is clearly visible;

• the flow of turning traffic is light;

• the turn only occurs from one lane;

• the speed of the turning traffic is low.

Full protection is necessary when any of thefollowing conditions apply;

• where there is a green arrow controlledconflicting left turn;

• sighting to the pedestrian crossing is restricted;

• the flow of pedestrians is high;

• the speed of the turning traffic is high;

• there is a high proportion of children, aged orhandicapped pedestrians;

• there are two or more lanes turning through thepedestrian movement.

Timed protection caters for any other situations.The length of the timed protection depends on thetype of pedestrians that are using the crossing, theflow of pedestrians and flow of conflictingvehicles, but it cannot exceed the duration of thewalk and clearance display.

18.9 Lanterns

18.9.1 Functions

To be effective, traffic signal lanterns mustcommand attention, convey a simple message andsatisfy the functions of:

• warning;

• stopping;

• starting;

• manouvering.

Primary (including dual and overhead) lanternsprovide the warning and stopping functions whilethe secondary and tertiary (including theoverhead) lanterns provide the starting andmanouvering functions as shown in StandardDrawing 1439.

These four functions are generally satisfied bythree lanterns per signal group for undividedapproaches and four for divided approaches. Theminimum is three per signal group for eachapproach and two for each supplementary turningmovement. Where possible, each lantern shouldbe used to fulfil more than one function, providedthat it is fully effective in its main function.

18.9.2 Assemblies

Lantern assemblies should be limited to no morethan six aspects (dual three aspect lanterns) perapproach on each post.

When a lantern consists solely of left or right turnarrows the lantern must never have all arrowsblacked out unless an adjacent three aspect lanternconsisting of full roundels is provided in the samedual lantern assembly.

Aspects are available in two sizes ie 200mm and300mm diameter.

Lanterns using 200mm diameter aspects areusually adequate as a warning or stopping signalon the primary and dual primary posts where theapproach speed is 70 km/h or less. Starting andmanouvering signals on the secondary and tertiary

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posts are normally only required to be visible overa little more than the width of the intersection andas this distance rarely exceeds 40m the standard200mm diameter aspects are usually adequate.

Lanterns using 300mm diameter aspects are usedon overhead signals mounted on mast armoutreaches. They may also be used in lieu of200mm aspects where a greater advance warningthen the normal is required.

A four aspect display consisting of red and yellowfull aspects and two green (full and arrow or twoarrows) in a single column display may be used.This is not permitted for overhead mountedsignals. Four aspect columns should not be usedin multicolumn displays.

18.9.3 Left Turn VehicleDisplays

18.9.3.1 Six Aspect Left TurnDisplay

Left turn movements can be controlled by a fullcolumn of left turn arrow aspects (adjacent to thestandard three aspect column) forming a sixaspect display.

The left turn green arrow aspect should beilluminated when no conflicting trafficmovements (vehicle or pedestrian) are permitted.

The left turn yellow arrow aspect followed by theleft turn red arrow aspect should be illuminatedwhen a conflicting movement must be protected.

The column of left turn aspects should be blackedout when the left turn movement may filterthrough a parallel walk or other traffic movementie the full aspect is green.

18.9.3.2 Five Aspect Left TurnDisplay

(a) Left Turn Yellow/Green Arrow Aspects

The red arrow aspect may be omitted from the sixaspect display when it is not required to protectconflicting movements during the display of the

full green. The left turn green arrow aspect shouldbe illuminated only when no conflicting trafficmovements are permitted.

The left turn yellow aspect provides a terminationdisplay to allow the left turn green arrow aspect tobe terminated independently of the full greensignal.

(b) Left Turn Red/Yellow Arrow Aspects

The yellow/red arrow aspects alone should beprovided when the left turn may be stoppedduring the full green display but the requirementsfor a left turn green arrow are not met. This occursinfrequently but may be required to stop left turntraffic for trains.

For left turning traffic a period must be assuredwhen the full green aspect is displayed alone.

18.9.3.3 Four Aspect Left TurnDisplay

(a) Left Turn Green Arrow Aspect

Use of a single aspect left turn green arrow aspectmay be used only when the green arrow is alwaysterminated simultaneously with the full greenaspect ie when the full yellow aspect isintroduced.

(b) Left Turn Red Arrow Aspect

Use of a single aspect left turn red arrow aspectmay be used only when its use is restricted todelay a 'filter' turn for protection of pedestrians inwhich case the red arrow should be switched offat the earliest practicable time eg at the end of thewalk period.

18.9.4 Right Turn VehicleDisplays

18.9.4.1 Six Aspect Right TurnDisplay

Right turn movements can be fully controlled bya full column of right turn arrow aspects (adjacentto the standard three aspect column) forming a sixaspect right turn display.

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The green right turn arrow aspect should beilluminated only when no conflicting trafficmovements (vehicle or pedestrian) are permitted.

The yellow right turn aspect should always beilluminated following the green aspect.

The red right turn aspect should be illuminatedfollowing the yellow aspect when the right turnmust be protected or when a conflictingmovement must be protected.

18.9.4.2 Five Aspect Right TurnDisplay

(a) Right Turn Yellow/Green Arrow Aspects

This display may be used instead of a six aspectdisplay when:

• the right turn movement may filter at all timeswhen the full aspect is green; and

• there is no conflicting pedestrian movement orspecial movement which requires protectionfrom the right turning vehicle.

(b) Right Turn Red/Yellow Arrow Aspects

This display is rarely needed. It may be used whenthere is no requirement for a protected right turnbut it must be stopped for its own safety eg by anearby train movement.

18.9.4.3 Four Aspect Right TurnDisplay

(a) Right Turn Green Arrow Aspect

This arrangement may only be used when thegreen arrow is always terminated simultaneouslywith the full green aspect eg in split phase.

A single column alternative (four aspect) can beused in this arrangement.

(b) Right Turn Red Arrow Aspect

Use of a single right turn red arrow aspect may beused only when its use is restricted to delay a‘filter’ turn for the protection of pedestrian orspecial vehicles.

18.9.5 Lantern Labelling

The labelling of lanterns is necessary todistinguish between different signal groups.

The vehicle signal groups are numbered inascending order with no gaps in the numberingsequence followed by the pedestrian signal groupsin ascending order with no gaps in the numberingsequence.

Individual numbering of signal groups for eachapproach improves the diagnostic process indetermining the cause of a short circuit and opencircuit in cables, terminals and lanterns.

All controllers with solid state lamp switching areequipped for lamp monitoring. The benefits ofthis will only be evident at STREAMS sites butintroduction of dial-up fault monitoring facilitiesto isolated sites is possible.

18.10 Detection

18.10.1 General

Traffic detectors are a primary requisite ofactuated signal control as they sense vehicular orpedestrian presence and/or passage and relay thedata to the local controller so that the appropriatesignal indications may be displayed for theirrequired initiation and duration.

Initial detection by arriving traffic faced by ayellow or red signal registers an initial demandthat it requires a green signal.

Subsequent detection by approaching traffic on agreen signal registers via the same system that itrequires the green signal to continue even thoughan initial detection may have been made by trafficon another approach.

18.10.2 Detector Types

The types of detectors currently in use are:

• vehicle detectors;

• push button detectors;

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• special detectors.

Vehicle detectors are the most common. The twotypes currently in use are the inductive loopdetector and the microwave (radar) detector. Themicrowave detector cannot detect stationaryvehicles and is only used at temporary signal sitesie bridgeworks. Push button detectors are usuallyprovided for the use of pedestrians.

18.10.3 Vehicle Detection

18.10.3.1 Characteristics

The inductive loop has proved to be the mostreliable vehicle detector. This consists of twoparts - a loop and a sensor unit. The loop consistsof turns of wire in a special pattern installed insaw slots in the road surface as shown in StandardDrawing 1424. These loops are connected to thesensor units normally located in the controller.

Traffic signal detection systems operate in twomodes:

• locking detectors detect the presence of amoving vehicle and are generally located inadvance of the intersection;

• non-locking detectors detect the presence of astationary vehicle and are generally locatedclose to the stop line on the approach to theintersection.

Locking detectors should produce a short pulse aseach vehicle enters the detection zone. Thereforethey allow a headway time. The only additionalinformation which a locking detector couldprovide is the flow rate. Locking detectors do notprovide further pulses if stationary (or very slowmoving) traffic occupies the detection zone.

Non-locking detectors should provide a continuousoutput while part of the vehicle is within thedetection zone. Therefore they can provide moreinformation than a locking detector enabling morecharacteristics of the vehicle stream to be calculatedeg besides indicating continuing presence of avehicle it also allows determination of occupancytimes. The non-locking detector is the preferredtype of detector for traffic management.

18.10.3.2 Installation and Location

Generally detectors should be located as shownon Standard Drawing 1425.

When locating detectors the following pointsshould be considered in regard to installation:

• does the pavement need resurfacing orreconstructing (loop wire is vulnerable todamage but needs to be close to the roadsurface for optimum sensitivity);

• loops cannot be installed over any bridges,culverts or similar structures unless there is atleast 80mm of covering pavement;

• loops cannot be installed closer than 300mm toany ferrous metal object such as a manholecover;

• the distance between the loop and the sensorunit is limited to about 300m and is dependenton the number of turns in the loop.

18.10.3.3 Types of VehicleDetectors

There are several types of vehicle detectors:

• advance

• stop line

• right turn

• counting

• queue

• violation.

18.10.3.4 Advance Detection

Advance detectors are so named because they arelocated in advance of the stop line. They are onlyused to detect moving vehicles and are thereforeoperated in passage mode.

Advance detectors should be used at sites wherethe approach speed is high and particularly if thereis a large proportion of heavy vehicles. Wherepossible they should be located to suit thestopping distance required for the 85th percentileapproach speed.

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Under free-flow conditions advance loops havethe advantage of being able to terminate phasesearlier since assessment of gaps or waste time canbe made several seconds before it can be detectedat the stop line.

18.10.3.5 Stop Line Detection

Stop line detectors are the most common and areso named because they are located at the stop line.They are always operated in locking mode.

Stop line loops require greater sensitivity as slowmoving or stopped vehicles must be detected. Thelocation of the loop in relation to the stop linemust be such as to ensure that a vehicle's normalstopping position is in the detection zone.

In addition the detector must have sufficientmemory time to monitor waiting traffic evenunder conditions of extreme congestion.

18.10.3.6 Right Turn Detection

Where a shared or exclusive right turn lanepermits filtering and a right turn phase is alsoprovided a right turn detector comprising threeloops connected in series and operating in non-locking mode is used. If necessary to achieve asatisfactory detection zone a fourth loop may beadded.

18.10.3.7 Counting Detection

Where connected to STREAMS extra loops tocount traffic may be provided eg auxiliary laneswith non-locking detection and uncontrolled sliplanes.

These detectors have no effect on the controlleroperation but use the controller's detector inputs.They are usually operated in locking mode.

18.10.3.8 Queue Detection

Queue detectors are used in special circumstancesto detect stationary vehicles for queue detectionand strategic purposes and must therefore beoperated in non-locking mode.

Typical applications include the detection of:

• traffic blocking an intersection;

• full or overflowing right turn lanes;

• queues on or near a rail level crossing adjacentto a signalised intersection;

• queues in a left turn slip lane with a heavy flowat a T intersection where the right turn flow islight.

18.10.3.9 Violation Detection

Violation detectors are installed in conjunctionwith a red signal violation camera and flash unit toenable red signal traffic violations to be detected.If a vehicle passes over one of the detectors whilefacing a red signal the camera and flash areactivated.

The camera equipment can accept up to four redinputs. This normally comes from the full redhence violation detectors should only be installedin lanes where all traffic is stopped by the full red.This includes exclusive through and right turnlanes and shared lanes where there is no left orright turn green arrow displayed in conjunctionwith the full red.

If the stop line is located at an angle then theshape of the loop is a parallelogram as it must beparallel to the stop line. This is the only type ofloop where this is permitted.

18.10.4 Pedestrian Push ButtonDetection

18.10.4.1 General

Pedestrian push button detectors are used toregister demands by pedestrians. They should beprovided on posts on each approach to apedestrian crossing.

Where a pedestrian crossing is interrupted by amedian they should be provided on any medianposts.

The push button should be mounted on the post1m above the level of the surface on which awheel chair stands when the occupant is

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attempting to use it.

Kerbside push buttons are generally oriented sothat the face of the assembly is at right angles tothe direction of travel. This orientation isimportant as visually-impaired pedestrians aretaught to determine the crossing direction byfeeling the face of the push button housingespecially audio tactile types. The push buttonsymbol on the drawing must be shown to thecorrect side of the post.

Mounting two push buttons on the one postshould be avoided.

18.10.4.2 Audio Tactile PushButtons

Audio tactile push buttons should be installedwhere they are needed by visually-impairedpedestrians. If an audio tactile push button isinstalled on a short post a note should be added tothe drawing to describe where the audio tactiledriver is located.

Audio tactile push buttons must not be installed:

• on median posts - except at 2 stage crossings;

• where there are two on the same post;

• within 2m of another audio tactile push button.

If necessary a short push button post may beinstalled to separate two audio tactile pushbuttons.

18.10.5 Special Detection

18.10.5.1 Emergency Vehicles

When traffic signals are close to a fire orambulance facility it may be necessary to takespecial precautions to ensure that emergencyservice vehicles are not blocked by stationaryvehicles and given right of way when trying toexit in an emergency.

Emergency vehicles are not normally detected byautomatic detectors. The appropriate Authorityprovides the necessary advance warning of theapproach of the vehicle and an emergency service

phase may be provided. A pedestrian push buttonis usually used as the detection device.

18.10.5.2 Rail level Crossings

If a traffic signal installation is located close to arail level crossing special provision should bemade to ensure that queues generated by thetraffic signals will not extend across the tracks.

If traffic signal linking with the level crossing isjustified track switches should be provided byQueensland Rail to enable a special queueclearing sequence to be initiated at apredetermined time before the train is due at thecrossing.

18.10.6 Detector Numbering

Traffic signal controllers have detector inputs thatare numbered. All detectors (including pushbuttons) on the drawing are numbered to indicatethese inputs.

In general the numbers for vehicle detection loopsare in ascending order from 1, starting from thecontroller and then in a clockwise direction.Counting detectors should follow after trafficsignal detectors ie advance, stopline and right turndetectors.

Numbers for pedestrian push button detection arein descending order from 16 or 32 depending onthe detector card used starting from the firstpedestrian group.

18.10.7 Detector Logic

Vehicles can be detected during two parts of thetraffic signal cycle. Traffic waiting for a greensignal registers an initial demand that it requiresright-of-way (call); and provided advancedetectors are no closer than 15m to the stop line,the controller can increment the initial green time.Traffic already given the right-of-way via a greensignal registers its continuing requirement forright-of-way so that the green signal can beextended depending on the prevailing trafficconditions (extend).

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Detector logic is used to specify the conditionsunder which an actuation from a detector can call,extend or increment a phase. For example thestandard detector logic for a stop line detector is:

• call a phase except while it is green;

• extend a phase while it is green;

and for an advance detector is:

• call a phase except while it is green;

• extend a phase while it is green;

• increment initial green except while it is green.

In the above logic there is only one phaseinvolved and only one condition for eachfunction. This amount of logic is sufficient for asimple two phase design but for most other typesof phasing several conditions may be required anda detector may demand and/or extend more thanone phase. When designing detector logic forthese situations the basic aim is to minimise thecycle time while satisfying all the traffic andsafety needs of the intersection. This is achievedby:

• avoiding the introduction of unnecessaryphases by only registering and maintainingdemands which are actually required:

• demanding a phase that satisfies the most (ormain) vehicle movements;

• minimising the variable initial green time byallowing detectors to increment when a queueis forming;

• avoiding unnecessary extension of a phase egby ceasing extension by vehicles on a givenmovement when that movement also runs in thefollowing phase.

18.11 Controller

18.11.1 General

The traffic signal controller is the equipment thatswitches power to the signal lanterns and controlsthe duration and sequence of the lantern displays.

Ground mounted interlocked and solid statecontrollers are utilised with operations ‘burnedinto’ an EPROM (Erasable Programmable Read-Only Memory).

18.11.2 Location

Controllers must be located so access can begained for maintenance purposes.

A ground mounted controller has only one doorfor access. This type of controller is normallylocated adjacent to the property boundary with thedoor opening towards the footway.

The location of the controller is also affected byother conditions. Ideally, the controller should belocated so that:

• a continuous 240v single phase power supplycan be conveniently obtained (some poles caterfor roadway lighting or high voltage supplyonly);

• a Telstra line is available nearby for STREAMScommunications;

• it is clear of high voltage poles and cabinetswith electrodes or earth grids as this can affectthe electronics in the controller;

• it is clear of future widening proposals;

• the position does not detract significantly fromthe visual quality of the streetscape (painting ina decorative way may be appropriate);

• there will be an unobstructed view of allapproaches to the site for timing andmaintenance purposes;

• it does not unduly obstruct the footway;

• it will not be unduly exposed to accidentaldamage by passing traffic;

• access is available for maintenance personnelto park a vehicle.

If it is located where it is vulnerable to traffic itmust be protected by appropriate safety barrier(see Chapter 8). It is preferable to find a less

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vulnerable location and thus avoid theintroduction of another hazard (safety barrier).

18.11.3 Full Actuated Control

In a full actuated application as used throughoutQueensland the controller operates oncontinuously variable cycle lengths. All phasegreen times are determined by the number ofvehicles detected on the various controlledapproaches.

The characteristics of full actuated control are:

• detectors on all approaches;

• each phase has preset minimum green intervalto provide starting time for standing vehicles;

• green interval is extended by preset passagetime for each actuation after the minimumgreen interval expires, provided a gap greaterthen the passage time does not occur;

• green extension is limited by preset maximumlimit;

• yellow change and all-red intervals are presetfor each phase;

• each phase has a recall when

- both recalls are off, the green will remain onone phase when no demand is indicated onthe other phase

- one recall is on, the green will revert to thatphase at every opportunity

- both recalls are on, the controller will cycleon a fixed-time basis in the absence ofdemand on either phase (one minimumgreen interval on each phase).

18.12 Electrical Design

18.12.1 General

Electrical design is required for power andlighting circuits for the interconnection of signalcomponents including controllers, lanterns,

detectors and push buttons. Cabling and wiringinvolved may provide one or more of thefollowing:

• 240V, 50Hz circuits for lamps;

• extra low voltage 50Hz circuits for pedestrianpush buttons;

• circuits for vehicle detector outputs;

• digital data links associated with co-ordinatedsignal systems.

Cable connection charts are required to identifyeach core of each cable, its function, connectiondetails and cable routing. Such a chart is anessential document for installation and subsequentmaintenance.

18.12.2 Installation

All cable systems shall be installed to therequirements of the Local Authority and ofAS/NZS 3000 - Wiring Rules. This provides forsafety for both electrical workers and the generalpublic. In this regard specific attention must begiven to:

• buried depth of cable;

• earthing of signal hardware and equipment forelectrical safety;

• adequate separation/isolation/insulation of240V and other cabling;

• jointing of cables at terminal strips located onthe top of signal posts, in junction boxes orwithin the cavity of joint use columns and mastarms;

• duct and access pit sizes to facilitate installationof cable.

18.12.3 Cables

Cables manufactured to the requirements ofAS2276 - Part 1 are used. For Departmentinstallations 6, 19, 29 or 39 core cables are used.

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For aesthetics and operational benefits cables areinstalled underground. Multicore cables have coreinsulation based on a four colour system asfollows:

(a) Earth core - Green/Yellow

(b) Neutral core - Black

(c) ELV return - Grey

(d) Other numbered cores - White

The number of circuits required will determinethe number of cores required in each cable.Provision must be made for:

• one active cable core for each colour of eachsignal group;

• one cable core for each pedestrian push buttoncircuit;

• a number of spare cores. Spare cores allow formodifications to the signal control modewithout recabling. In the event of core damageit may allow repair to be carried out without theneed to replace the cable.

18.12.4 Vehicle Detector LoopCables

The feeds to vehicle loops should be screenedfeeder cable manufactured to the requirements ofAS2276 - Part 2. Single or three pair twin 7/0.50cable is used.

The sensor to loop distance should be minimised(300m maximum) since long lengths of feedercable may have adverse effects on detector sensoroperation.

The loop cable should be manufactured to therequirements of AS2276 - Part 3. Single 7/0.50cable is utilised.

18.12.5 Data Link Cables

Data link cables are leased from Telstra.

18.12.6 Cable Connection Design

The cable connection design determines the size,length and routing of cables. The circuitsconnecting lanterns, push buttons and waitindicators to the controller may be optimised toproduce the most economic solution.

The number of cores in the multicore cable ischosen to provide sufficient circuits for eachcolour of each signal group and push button. Thecores are connected from the post mountedterminal block on each post or terminal strip ineach joint use or mast arm to the controllerterminals.

The cable connection chart documents the cableconnection design. Details of the connection ofindividual cable cores to the appropriate terminalsin the controller and on each terminal block ateach post, joint use pole or mast arm are shown.

18.12.7 Adaptive Engineering

The task of configuring of a controller to thespecific requirements of a particular site is knownas adaptive engineering. It includes the provisionof phasing, sequencing signal groups and theprevention of hazardous displays.

Hazardous displays arise from failures in themechanisms that switch power to the signallanterns. These hazards can be minimised byinterlocked switching and/or conflict monitoring.

Interlocked switching is used with relay switchingof lamp circuits eg Philips PTF controller. Thegeneral principal is that switching a green to onesignal group will open the circuit to conflictinggreen signal groups and close the circuit to the redof these signal groups.

One method of interlocking signal groups iseffected by connecting relay contacts in series tocreate a ‘chain’ from the lamp active supply to thegreen feeds of the signal groups. When a signalgroup is switched to green the green feed to signalgroups lower down the chain is open circuited(green interlocking). The groups that are higher inthe 'chain' must ensure red is displayed for groupsthat are lower in the 'chain' (red interlock). Signal

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groups that are designated to have an “off” displayshould be in the lowest positions in the 'chain'.They do not require a red interlock as this wouldoverride the off display.

Conflict monitoring is mandatory where solidstate lamp switching is used eg Tyco PSC orAldridge ETG controllers. The circuits to thesignal group colours should be monitored as closeas possible to the controller output terminals. Thestate of each circuit is compared with thepermissible and the unsafe states determinedduring the adaptive engineering (conflict table) toprevent unsafe operation.

18.13 Co-ordination

18.13.1 General

Traffic signals co-ordination is implemented toimprove the level of service of a road or a networkof roads where the spacing of signals is such thatisolated operation causes excessive delays, stopsand loss of capacity.

Co-ordination maintains a time relationshipbetween adjacent sets of signals. This ispredetermined to achieve the design objective ofminimising overall delay and/or the number ofstops. All signals to be co-ordinated must operateat the same cycle time to maintain the requiredtime relationships. An exception to this cansometimes be made when it is found that a cycletime of half the system cycle time at some signalscan reduce delay to the side road traffic withoutunduly affecting main road performance. This isknown as double cycling.

Co-ordination is also used to assist in theachievement of other traffic management andenvironmental objectives such as improving thelevel of service of arterial roads to reduce thepressure on residential streets.

The benefits of traffic signal co-ordinationinclude:

• improved capacity of closely spaced signalisedintersections;

• reduction in travel time and delay;

• reduction in number of stops;

• reduction in intersection accidents;

• reduction in noise levels, air pollution andenergy consumption;

• achievement of other area or corridor trafficmanagement goals.

18.13.2 The Case for Co-ordination

An isolated intersection is one in which vehiclearrival at each approach is not significantlyaffected by other intersections. This situation canbe managed by traffic actuated controllers with ahigh degree of efficiency.

The presence of a nearby signalised intersectionor a pedestrian crossing upstream of theintersection alters the arrival pattern from randomto platoon flow. This enables improved trafficflow to be achieved if the green signal is arrangedto coincide with the arrival of the platoon.

The closer the traffic control signals are spacedthe less random the arrival patterns become andthe greater the opportunities are for improvedefficiency afforded by co-ordination. Generally,when traffic signals are provided at successiveintersections spaced less than one kilometre apart,benefits result from co-ordination. At spacings ofless than 500 metres the reductions in delays andstops usually exceed 20%.

18.13.3 Types of Co-ordination

There are numerous options available for signalco-ordination. These options fall into three basiccategories, namely local co-ordination, mainsfrequency or cableless link co-ordination andcentrally controlled co-ordination (STREAMS).Local and mains frequency co-ordination systemsare rarely used.

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18.13.3.1 Local Co-ordination

With this type of co-ordination the localcontrollers in a system are free within certainconstraints to respond to specific traffic demands.

Local co-ordination may be implemented usingone or a combination of the following:

(a) Sister Linking - a simple method ofachieving vehicle progression between twoor three intersections that are less than 300mapart. The main linking mechanism is theestablishment of a time relationshipbetween the commencement of thecontrollers maximum green timers ortransfer of detector actuations from each siteto the other (repeat pulsing) by a cableconnection between the sites.

(b) Master/Slave Link - this is a system inwhich a number of controllers areinterconnected such that one of thecontrollers takes the role of masterdetermining cycle time and phase times forthe group and all other controllers aresubservient to the operation of the mastercontroller.

(c) Vehicle/Pedestrian Link - this is used to co-ordinate a closely spaced (generally 200mmaximum) mid block pedestrian crossing toan intersection by means of a cableconnection. The pedestrian site is inhibitedfrom going to the pedestrian phase until thevehicles from the intersection have clearedthe pedestrian site. There are two types oflink. One specifies a vehicle phase underwhich a pedestrian phase should run and theother a vehicle phase under which apedestrian phase should not run.

18.13.3.2 Mains FrequencyCo-ordination

With mains frequency or cableless link co-ordination the controller responds to inputs fromvehicle and pedestrian detectors and from pulsesgenerated by the co-ordination software residentin the controller. Co-ordination timing plans arechanged by time of day and day of week.

The 50Hz electricity supply provides an accuratetime base to maintain fixed time relationshipsbetween controllers. Clock times must beregularly checked on site and adjusted ifnecessary to ensure that clock times are accurateand all clocks are synchronised so that the offsetsmaintain the correct time relationship for the co-ordinated route.

18.13.3.3 Centrally Controlled Co-ordination

Where sites in a system are all connected to aSTREAMS regional computer the local controllermay operate under the following conditions:

(a) Isolated - operates as any other isolated siteexcept that it can respond to the STREAMSspecial facility signals and can be monitoredby the regional computer eg monitoring oflamps, changing time settings, vehiclecounts and special facilities enabled ordisabled.

(b) Flexilink - is the same as cableless linkoperation except that the clock times in thecontroller are kept accurate by regularreference to the time obtained from theSTREAMS regional computer.

(c) Masterlink - allows full dynamic control bythe STREAMS regional computer. The datagathered from strategic detectors are used tooptimise the cycle time and the phase splitsfor each intersection in the sub-system. Inthe event of a communication fault betweenthe controller and the STREAMS computeror failure of the STREAMS computer thelocal controllers automatically revert to thefallback mode of operation. The fallbackmay be isolated or flexilink.

18.13.4 Design Factors

The routes and/or networks to be co-ordinatedmust be decided and the following factorsconsidered:

(a) Roadway - information is required on thecapacities of roads both at and between

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intersections. This enables an assessment ofthe manner in which traffic platoons willbehave. The effective capacity of the co-ordinated system is determined by thecapacities of the critical intersections thatmust be identified. In addition data on thegeometry of the intersections in thenetwork, including the location of existingand planned intersections and pedestriancrossings, and the distances between thestop lines of the intersections is required.

(b) Geometric - examination of intersection androadway geometry may indicate the needfor changes to improve the flow of traffic.Examples of geometric improvementsinclude the provision of protected right turnlanes, free left turn lanes and linemarkingalterations to minimise lane changingcaused by lack of lane continuity along aroad.

(c) Traffic - a complete inventory of trafficmovements along a route to be co-ordinatedis required. This enables time-distancediagrams and signal timing plans to beprepared. Individual intersections must beassessed first after which appropriatecombinations of intersections may beassessed on a co-ordinated basis usingcommon cycle time.

(d) Equipment - an inventory of existingequipment is necessary to identifyconstraints imposed by this equipment anddetermine required changes.

18.13.5 Requirements for SignalDesign

When undertaking the design of a set of trafficsignals it is important to consider the effectswhich co-ordination will have on the design. Themajor effects relate to:

(a) Controller Selection - the use of controllersthat are compatible with the type of co-ordination adopted.

(b) Detector Loops - consideration of thedetection system required which in many

cases will be specified by the type of mastercontrol system to be installed. Detectorplacement and function options includeindividual lane detectors, advance detectors,stop line detectors and queue detectors.

(c) Cycle and Phase Timing - a common cycleor sub-multiple of it is required for co-ordinated systems. The system cycle timewill be that of the most critical intersectionin heavy traffic or derived from travel timeto achieve two-way progression undercertain traffic conditions. Phase splits atcritical intersections must normally followthe minimum delay criterion ie greenterminates when the queue has dissipatedotherwise residual queues form with anexcessive delay penalty. Non criticalintersection phase timing may be adjusted toreduce stops or it may be beneficial to'double cycle' the intersection.

(d) Phasing - the phasing design of signalsneeds to consider the co-ordinationrequirements. For example it may benecessary to vary the phase sequence toachieve two-way co-ordination or useleading and trailing turns during peakperiods.

(e) Side Road and Pedestrian Delay - atintersections in a co-ordinated system therecould be an increase in delays to vehiclesentering from side roads and pedestrianscrossing the main route compared withoperation on a traffic actuated basis.Therefore careful consideration must begiven to this factor to ensure minimisationof this adverse effect. This effect will bemore prevalent with fixed plan systemswhere limited plans are available on a 'timeof day' basis compared with trafficresponsive systems. It may be beneficialunder light flow conditions to revert toisolated traffic actuated operationparticularly where the spacing betweenintersections is such that two-wayprogression cannot be attained at a lowcycle.

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(f) Public Transport - the needs of publictransport should be considered in the overalldesign. Benefits to public transport may beachieved by either introducing a passivebias to the signal settings or by activelyresponding to the presence of a publictransport vehicle to adjust the signaloperation. It may also be possible to relocatebus stops at certain critical points.

18.13.6 Timing Criteria

Earlier research suggested that the principalcriterion for co-ordination timing is minimumoverall delay. However, subsequent experiencehas indicated that this criterion does not takeadequate account of the following three factors:

• accident risk - this is the greatest at the changeof signal phases and is reduced if fewervehicles are stopped;

• fuel consumption and exhaust pollution - this isincreased by repetitive driving cycles (stop-start driving);

• driver expectation - drivers relate co-ordinationmore to the number of stops than to overalldelay.

The current criteria for co-ordination timing aretherefore biased towards minimising overall stopsand fuel consumption. This does not yield thesame signal timing plans as the minimum delaycriterion due to the different offsets necessary anda general requirement for longer cycle times.

For co-ordinated traffic systems several methodsof designing signal timing plans are available:

• time distance diagrams manually prepared;

• computer programs such as TRANSYT orSCATES can be used to optimise timing plansaccording to traffic flow data entered forvarious times of day.

18.14 Mid-Block PedestrianCrossings

18.14.1 General

Once the decision to provide a signalised mid-block pedestrian crossing is made, the designermust choose the type of crossing and the bestlocation for it.

Signalised mid-block pedestrian crossings mustbe located a minimum of 30m from any sidestreets. This is to avoid side street trafficmisinterpreting the traffic signals as controllingtheir movement. It also prevents the situationwhere a vehicle enters the main road just as thesignals change to the pedestrian phase and thedriver of the entering vehicle is unaware of thechange or unable to react in time.

Signalised mid-block pedestrian crossings shouldalso be avoided within 130m of an adjacentsignalised intersection.

18.14.2 One Stage Crossings

A one stage crossing is used on roads where thereis no median or the median is less than 4m wide.Where there is a median then median lanternsneed to be provided. Push buttons may beprovided if required.

18.14.3 Two Stage (Offset)Crossings

The installation of a signalised one stagepedestrian crossing on carriageways with widemedians (4m or more) may cause excessivedelays resulting from lengthy pedestrian clearancetimes. At sites where long pedestrian crossings area problem, a two stage crossing should beconsidered. This allows traffic signal co-ordination under STREAMS and reduces trafficdelays. Two stage crossings may be needed inother circumstances with medians as narrow as2.0m. The crossing point must be flush with theadjacent pavement surface in those cases.

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Figure 18.18 Two-Stage Mid Block Crossing (LHOffset)

The kerbside pedestrian lanterns must be aimed sothat they are not visible to pedestrians on theopposite side of the road. A physical barrier ofsuitable fencing should be provided on the medianto prevent pedestrians from ‘short cutting’between the crossings. Fences should be alignedso that pedestrians face oncoming traffic as theyare about to leave the median. The fences shouldcommence at the signal post and not encroach pastthe push button position.

Intervisibility, as well as the physical layout of thefence, are very important and should be majorfactors in deciding whether pedestrian fencesshould be installed.

Particular attention should be given to the heightand placement of the fence, and to the materialused in its construction, in order to minimise thepotential sight obstruction between drivers andpedestrians about to cross the road. Improperinstallation or rehabilitation of pedestrian fencescan effectively negate any potential increase inpedestrian protection and can also increase theseverity of vehicle accidents.

Fencing with rigid horizontal railing, installednear roads can be a hazard to occupants of errantvehicles. The horizontal rails can easily becomedetached and spear into the driving compartment.

18.15 Special Situations

18.15.1 Emergency ServiceFacilities

When traffic signals are close to a fire orambulance facility it may be necessary to takespecial precautions to ensure that emergencyservice vehicles are not blocked by stationaryvehicles when trying to exit in an emergency. Thiscan be achieved by using traffic managementtreatments such as:

• relocating the stop line further from theintersection;

• installing warning signs and flashing lights;

• adding a special emergency vehicle phase.

Relocating the stop line could be appropriatewhere the emergency vehicle egress is at theintersection. If the resultant position of the stopline is “unnatural” from the motorist's point ofview extra facilities such as signs (eg STOPHERE ON RED SIGNAL R6-6) may benecessary.

When the exit from the emergency service facilityis more than 10 metres from the intersection andrelocation of the stop line would require a longerintergreen period, warning signs with flashingyellow lights may be located at the exit. These areoperated from the facility to allow safe egress forthe emergency service vehicles. It may also beappropriate to provide signs and/or pavementmarkings to warn motorists not to queue acrossthe driveway.

An emergency vehicle phase may be introducedwhere emergency vehicle turnouts provide entrydirectly to a road adjacent to signalisedintersections based on the:

• conflict between emergency vehicles and othertraffic;

• possibility of queued vehicles blocking the exitfrom the emergency service facility;

• delays to emergency service vehicles if theemergency service phase is not provided;

2.0m minimum

Desirable 2.0m minimumoffset between crossings

3.0m

Fencing

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• effect on traffic flow.

The emergency service phase should clear anyqueued vehicles within the path of the emergencyservice vehicle to allow it unimpeded travel in anydirection through the intersection. Again thefacility to activate the emergency vehicle phase isprovided within the service facility.

At isolated mid-block emergency vehicleturnouts, signal facilities activated within thefacility may also be provided. Emergency vehiclesignals are two aspect consisting of a 300mmdiameter red and yellow lantern with a targetboard. Overhead emergency vehicle signals arealso provided for either of the following:

• restricted visibility of emergency vehiclesignals;

• very wide carriageways.

Overhead emergency vehicle signals are not usedwhere such signals are located adjacent tointersection traffic signals. In these circumstancesthe need for overhead signals or additionalmeasures is determined in relation to theintersection traffic signals.

At the emergency vehicle turnout the followingare provided:

• emergency vehicle signals;

• STOP HERE ON RED SIGNAL sign (R6-6);

• stop line marking.

Where the stopping distance on the approach tothe emergency vehicle turnout is restrictedflashing yellow aspects are mounted inconjunction with the advance warning signEMERGENCY VEHICLES (W5-26-1). Theselanterns are 200mm in diameter.

18.15.2 Adjacent Rail LevelCrossings

If a traffic signal installation is located close to arailway level crossing, special provision should bemade to ensure that queues generated by thetraffic signals will not extend across the rail tracks

and queues generated by the rail crossing will notextend into the intersection.

If traffic signal linking with the level crossing isjustified, track switches are provided byQueensland Rail to enable a special queue-clearing sequence to be initiated at apredetermined time before the train is due at thecrossing. The track switches should also indicatewhen the train has cleared the crossing. The trafficsignal requirements should be determined inconsultation with Queensland Rail during thepreliminary design stage.

If the level crossing is fitted with flashing redsignals, the queue-clearing sequence should beinitiated. The queue clearing sequence shouldforce the traffic signals to a phase which will clearthe queue across the level crossing before thearrival of the train.

Once the queue clearing phase has terminated, nophases or turning movements which would crossthe rail line can be introduced until the train hascleared the crossing. It may be necessary toprovide for additional storage of these vehicleswhile the level crossing is closed.

In some situations it may be possible to includethe level crossing within the vehicular conflictarea. In this case, the train movement may betreated as a priority phase.

Special precautions will need to be taken to ensurethat green traffic signal aspects are not visibleacross the level crossing at the same time as theflashing red rail signals. Similarly, thepositioning, screening and aiming of vehiclelanterns must be arranged to ensure that trafficsignals do not cause confusion to train drivers.

18.15.3 Early Cut-Off Facilities

The early cut-off period is normally used toterminate one movement before another withinthe same phase. A typical application of this is atstaggered T- junctions as shown in Figure 18.19.

In this example there are two A phase stop lines ineach direction. The A(ECO) signal group is thefirst to display a yellow aspect. The A signal

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group remains green longer to allow the section ofroad between the stop lines to be cleared.

Figure 18.19 Staggered T-junction

Note that this example is simplified in order todescribe the principle and would only be used ifthe number of right turn vehicles from the sidestreet is particularly low. In practice, if the zig-zagmovement is dominant, the left turn movementsfrom the main road would be permitted during Bphase. Otherwise the side streets would more thanlikely have separate phases. This would result in anumber of conditional early starts and conditionalearly cut-offs.

18.15.4 Interchange Ramps

A very efficient signal design for an interchange isthe “Fast Diamond” where all ramps areconcentrated at one signalised intersection asshown in Figure 18.20. This enables the use of asingle or double diamond overlap. However, careshould be taken when selecting turning radii toensure that the opposed right turns have sufficientclearance to allow the safe operation of thediamond turns (see Chapter 13).

Figure 18.20 Typical SIngle Point Urban, “FastDiamond”, Interchange

Care should be taken to ensure that the longdistance between stop lines does not create unsafeconditions. This is particularly so where apedestrian crossing and/or a distant startinglantern may cause drivers who cross the stop lineat the start of the intergreen to hesitate beforeclearing the intersection.

This type of interchange is usually much moreexpensive than the traditional type because ofadditional bridge costs (see Chapter 16).

For closed diamond interchanges, the interchangeramps are separated into two intersections asshown in Figure 18.21. The intermediate stoplines provide safe stopping for slower movingvehicles and enable a reduction in the intergreentime. The two sites may be controlled by one ortwo controllers. If one controller is used (usuallyto save costs) the site can have phase options toallow some flexibility in operation. If twocontrollers are used the sites can be co-ordinatedto provide progression.

When two intersections are used the spacing ofthe intersections needs to be carefully designed toensure that adequate storage is provided for theright turn vehicles. Storage requirements can beminimised by proper utilisation of the early cut-off interval.

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Figure 18.21 Typical Diamond Interchange

When one controller is used, the early cut-offinterval may be used in a similar manner to astaggered T-junction. In this case some of themovements may be allowed to start early inassociation with the early cut-off of anothermovement. This is known as an early start (ES).An example of this is shown in Figure 18.22.

Figure 18.22 Early Start at Interchange Ramps

In this example, when A phase is followed by Bphase the A(ECO) signal group turns yellow at thecommencement of the A phase early cut-off greeninterval. At the end of the yellow the A(ECO)signal group turns red and the all-red timer isstarted. When this timer expires the B(COND ES)signal group displays green. This is permittedbecause the A(ECO) signal group has clearedtraffic from the conflict area. When a signal groupis allowed to display green at the start of theyellow interval this is known as green on yellow(GOY).

Note that this example is simplified in order todescribe the principle and would only be used ifthe number of right turn vehicles from the freewayramps is sufficiently low to allow storage betweenthe two stop lines. In practice, it would normallybe more efficient to run all through movements onthe main road during A phase and provideseparate phases for all other right turns. Thiswould result in a number of conditional earlystarts and conditional early cut-offs.

18.15.5 Ramp SignalManagement

18.15.5.1 General

The Ramp Signal Management service isresponsible for all functions relating to rampsignals on freeway on ramps. These functionsinclude the following:

• management of the descriptive andconfiguration data for the ramp signal;

• specification of recurring schedules. Theseallow scheduling of ramp signal flows by timeof day on a special date. A special time-of-dayflow introduction schedule may be used foreach ramp signal. The schedule should coverthe flow introductions required for a specificdate. This schedule has a higher priority than arecurring schedule;

• processing of traffic-responsive requests fromthe movement service. These requests resultfrom calculations based on current trafficconditions on the freeway and the ramp andaim to avoid congestion on the freeway. Theserequests are higher priority than the recurringand special schedules but lower priority thanoperator manual control;

• implementation of operator override requests.These requests allow the ramp signal flow to becontrolled manually by the operator. This is thehighest priority form of control. The flow willbe implemented for the defined period and thenautomatically be replaced by the next highestpriority form of control;

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• reporting of operations of metered movementsand their associated ramp signals. Screendisplays and printed reports are available;

• managing the specific data history.

18.15.5.2 Ramp Metering

The primary purpose of the service is to ensurethat ramp metering is active when it should be andthat the appropriate metering rate is implemented.The desired metering rate is achieved by adjustingthe time that the red lamp is displayed in eachcycle (the time that the green lamp is displayed isconstant and it is determined by the Green TimeParameter).

When the service determines that a particularmetering rate is to be implemented it calculatesthe required red time according to the followingformula (which assumes that only one vehicle perlane is admitted each cycle);

Red time = (3600/metering rate) - green time

Where Metering Rate is the desired rate invehicles per hour per lane, andGreen Time is the time (in seconds)specified by the Green Timeparameter.

Example:

If a metering rate of 600 vehicles per hour is to beimplemented on a ramp with two lanes at the stopline and the green value parameter is 1.7 seconds,the red time is calculated as follows:

Metering Rate = 600 / 2= 300 vehicles per hour per lane

Red Time = (3600 / 300) - 1.7= 10.3 seconds

Provided the calculated Red Time value isbetween the limits specified by the Minimum RedTime and Maximum Red Time parameters thedesired metering rate can be implemented.

The parameters Green Time, Minimum Red Timeand Maximum Red Time determine the minimumand maximum metered rates (per lane) that can beachieved by any metered ramp on the system.

Although it is possible to specify minimum andmaximum metered rates for each metered rampthey must lie within the range determined by theseparameters.

Requests for metering (or to turn off metering)can come from any of the following sources:

• recurring schedule;

• special schedule;

• traffic responsive;

• operator override.

The service is responsible for evaluating andimplementing these requests and, where conflictarises, deciding which request is to be acted on.This decision is based on the predefined priorityordering assigned to the different types. Thisordering, from highest to lowest priority, is:

• operator override;

• traffic responsive;

• special schedule; and

• recurring schedule.

18.15.5.3 Reports

Operations reports can be produced showing theoperation of each metered movement and itsassociated ramp signal.

The current values of each of the following itemsare shown on the report for each meteredmovement:

• metered rate (if currently metered);

• level of service;

• demand;

• capacity;

• flow (last minute);

• control type;

• metering state;

• signal state; and

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• red time.

Trend reports show a graphical trend of theoperations history of a metered movement and itsassociated ramp signal.

Selection for graphing of several ramp signalsettings and also various traffic measurements forthe metered movement and the adjacent upstreamand downstream freeway movements is possible.

The resulting plot shows how these settings andmeasurements vary with time for the specifiedmovement and report period.

Items included in the plot are selected from thefollowing:

• metered rate;

• control type;

• traffic responsive rate;

• downstream level of service;

• on ramp demand;

• on ramp capacity (expected);

• on ramp flow (last minute);

• bypass flow (where a bypass movement exists);

• total flow (where a bypass movement exists);

• downstream flow;

• downstream capacity;

• upstream flow;

• upstream demand.

18.15.6 Roundabout EntranceMetering

Roundabouts will not function efficiently if thereare insufficient acceptable gaps in the circulatingtraffic stream. If there is one approach with a veryheavy through or right turn movement, which isnot interrupted sufficiently by the circulatingflow, then this stream will present few acceptablegaps to drivers at the next entry. The capacity ofthis entry will be very low and the delay to this

traffic excessive. Often this situation occurs onlyduring peak flow periods and at these times theoperation can be dramatically improved byartificially interrupting the high flow approach.

Entry metering is usually done by installing trafficsignals to meter the flow as it approaches theroundabout. This has the effect of bunching theflow of traffic and introducing more of the longerduration gaps. It is important not to locate thesignals too close to the entry as this may confusethe 'right of way' requirements at the entry.

Two-aspect signals (red and yellow only) are usedwith a STOP HERE ON RED SIGNAL (R6-6)sign provided.

Signalisation of roundabouts is not considered tobe a long term solution to the relief of congestionand excessive delays due to normally increasingtraffic volumes. Conventional signalisedintersection layouts or a grade separated treatmentwill generally be a more effective long termsolution.

18.15.7 Late Start for LargeCorner Islands

In addition to the uses of the late start described inSection 8.5 the late start interval may be used todelay the introduction of a green signal group at acontrolled left turn slip lane where there is a largecorner island as shown in Figure 18.23.

In this example the B(LS) signal group is held redfor the B late start interval. This allows the Aphase vehicles to clear the conflict area before theleft turn is introduced.

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Figure 18.23 Late Start for Large Corner Islands

18.15.8 Temporary Installations

18.15.8.1 Portable Traffic Signals

Portable traffic signals are a short-term trafficcontrol application. Their primary use is as ashuttle control where a portion of the roadway hasbeen closed and a single lane is used alternatelyby traffic approaching from the oppositedirections.

The standard equipment currently used by MainRoads in Queensland is not designed forunattended or overnight operation. The typicalset-up does not provide sufficient redundancy toensure safe operation when unattended. Whereunattended or overnight operation is required,temporary traffic signals should be used.

Where circumstances arise where it isimpracticable for temporary traffic signals to beinstalled, it is essential that the installation bedesigned to provide a sufficient level of

redundancy and that operational procedures beestablished to provide assurance that continuouscontrol will occur. When determining theappropriate equipment and operational proceduresto adopt, the following factors for each site mustbe considered:

• Traffic volumes;

• Length of single lane operation;

• Visibility along the section of road;

• Risks of signal failure and the consequences;

• Availability of power;

• Call-out/ maintenance arrangements and costs.

In general, unattended operation should not beconsidered where the whole section of single laneis not visible from both ends by approachingdrivers.

In any case, if the operation is to continue for anextended period, temporary traffic signals shouldbe installed as described in 18.18.8.2.

18.15.8.2 Temporary Traffic Signals

When a road or bridge is under repair orreconstruction for longer than three months and along stretch of one lane road is used alternately bytraffic approaching from opposite directions,temporary traffic signals can sometimes be usedas a control. The general treatment in this instanceis to use two phases where one phase controlseach direction. Unfortunately, this requiresextremely long intergreen times to allow onemovement to clear the conflict area before theother movement can be started. This causeslengthy delays which could lead to driverfrustration. This cannot be avoided in heavytraffic situations but the overall delays can beminimised in low traffic situations by adding anall-red phase as shown in Figure 18.24. Thecontroller will normally wait in the all-red phaseuntil one of the other phases is demanded. Thatphase can then be immediately introduced withminimum delay to the motorist. The phase isextended and terminated as usual.

B (LS)

A

B

A phase B phase

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Figure 18.24 All-Red Phase at Temporary Signals

18.16 Time Settings

18.16.1 General

This section provides procedures and states policyfor the calculation of various traffic signalcontroller times.

These times are required as data for all trafficsignal controllers.

The controller times in this section are generallythose which directly affect the safety of theoperation of the intersection eg intergreen,minimum green and extension times. No guidancefor the calculation of operational time data such ascycle times, green splits or offsets which aregenerally calculated using traffic engineeringprinciples are provided.

The times are usually applicable to each phase ofthe cycle and some may be individually set foreach movement within the phase. The availabilityof the settings may be dependent on the type ofcontroller used.

18.16.2 Yellow and All-RedTimes

18.16.2.1 Policy for ClearingInterval

MUTCD Section 14 Appendix A3.3.1 gives thecurrent policy for the clearing interval as follows.

The vehicular clearing interval is indicated by asteady yellow aspect for a period ranging from 3to 5 seconds and shall be provided in accordancewith the following:

i. Speed limit up to and including 60 km/h - 4seconds;

ii. Speed limit between 60 km/h up to andincluding 80 km/h - 5 seconds;

iii. Yellow arrow aspect which operatesindependently of a through movement onthe same approach, at all times, and which isalways followed by a phase for theassociated through movement - 3 seconds.

The yellow interval is followed by a short all-redinterval of sufficient duration to provide for thesafe clearance of vehicles which have lawfullyentered the intersection during the yellow interval.The minimum all-red interval shall be 1 second.

The pedestrian and bicycle clearing intervals areindicated by the red symbolic standing pedestrianand red symbolic bicycle aspects respectively.These aspects may be shown flashing.

18.16.2.2 Calculation of YellowTimes

The purpose of yellow time is to provide a safetransition period before the start of the next phase.

The yellow time is set for each phase withreference to vehicle speeds for each movementthat stops when that phase terminates. Vehiclespeeds are considered in two ranges (Clause18.16.2.1) and the applicable range is normallytaken to be the range that includes the legal speedlimit for that approach.

If the phasing is such that the only movement thatis stopped when a given phase terminates is a rightturn movement and there is no possibility that thecontroller will allow a different phase sequencewhich will result in other movements stoppingwhen the phase is terminated, then the yellowtime for the phase may be terminated by the rightturn movement (3 seconds).

18.16.2.3 Calculation of All-RedTimes

The purpose of the all-red time is to provide a safeclearance time for vehicles that legitimately enterthe intersection during the yellow interval.


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The initial settings of all-red time can becalculated as:

• d/14 seconds in 60 km/h zones (up to 60 km/h);

• d/21 seconds in 80 km/h zones (between 60 and80 km/h).

where d = distance, in metres, from the approachstop line to clear the farthest conflicting point ofany opposing traffic stream (including pedestriancrossings) which can operate in the next phase.

Note that consideration must be given to thepossibility that the next phase may vary withtraffic demand or sequences selected for co-ordination and the highest value for the all-redtime should be used.

Final settings of all-red times should bedetermined on site by a visual assessment ofclearance times required by vehicles thatlegitimately enter the intersection during theyellow interval.

It is possible to set all-red times to the nearest 0.1second but settings of not less than the calculatedvalue or more than the calculated value +0.5seconds should be used without full investigationof operations on site and with due authority.

The minimum all-red time shall be 1.0 second.

It should be noted that no additional all-red timeshould be provided to clear vehicles waitingwithin the intersection to make a right turn.

18.16.3 Other Vehicle Times

18.16.3.1 Late Start Period

The purpose of the late start period is to allow thedelay of the introduction of specific signal groupsfrom the start of a phase by a preset time.

Typical settings are:

• to delay left turns by 3 to 8 seconds dependingon intersection geometry;

• to delay filtering right turn by 5 seconds.

18.16.3.2 Minimum Green Period

The purpose of a minimum green period is toensure that the green signals are always displayedfor a safe minimum time. This time should belong enough for a single vehicle to start up andenter the intersection.

A typical setting is 5 seconds.

The minimum green period and the increment(Clause 16.3.3) are used to determine the variableinitial green (Clause 16.3.5). The variable initialgreen cannot be less than the minimum greenperiod.

18.16.3.3 Early Cut-Off GreenPeriod

The purpose of the early cut-off green period is toallow the early termination of the green signals toone or more movements within a phase by theearly introduction of the yellow and all-redperiods to these movements only.

Settings are dependent on intersection geometrybut not normally less than 3 seconds.

18.16.3.4 Increment

The purpose of increment is to increase the initialgreen time beyond the minimum green time toensure adequate green time for vehicles queuedbetween the detector loop and the stop line.

For vehicle approaches or movements on anapproach where vehicles can queue between thedetector loop and the stop line each vehiclearriving against a red signal will add a smallamount of time (an increment) to the minimumgreen time.

A typical setting is 2 seconds.

This setting should be increased for upgrades anddecreased for downgrades at the rate of 0.1 secondper percent of grade. Values should be verified byobservation on site under the full range ofoperational conditions especially where laneutilisation varies or vehicle counts are collectedfrom more than one lane.

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18.16.3.5 Maximum Variable InitialGreen

The purpose of maximum variable initial green isto limit the initial green period determined byincrements.

Settings are dependent on the distance betweenthe detector loops and the stop line. For example,if the distance is 40m, then for an assumedoccupancy of 6m per vehicle the maximum queuewould be 7 vehicles in each lane. Assuming avehicle leaves this queue every 2 seconds whenthe signal turns green then the required setting is(7 x 2) = 14 seconds.

Careful site observation is required to ensure thatthere is sufficient variable initial green time sothat vehicles queued beyond the detector loopscan move over them and thus extend the phase.

18.16.3.6 Gap Timer

The purpose of the gap timer is to control themaximum allowable time period betweensuccessive detector actuations before themovement terminates.

If the gap timer is too short the movement mayterminate before the platoon has passed. If the gaptimer is too long the movement may be extendedunnecessarily.


• 3 seconds for presence detectors (as used forright turn lanes where the movement is allowedto filter);

• 4 seconds for normal detectors.

Note that current microprocessor controllersprovide for at least 2 and up to 8 gap timers so thatdifferent approach characteristics such as gradeand turning radii can be catered for.

18.16.3.7 Headway (Space) Timer

The purpose of the headway timer is to set thedesirable time period between successive detectoractuations for efficient traffic flow so that the

running phase is terminated if this flow is notbeing realised on any approach.

A typical setting is 1.25 seconds.

If detector zone length is taken as 3 x detectorlength ie 3 x 4.5m = 13.5m, vehicle occupancytime will be 13.5/speed (m/s). For a saturationflow of 1700 veh/h the headway time is3600/1700 = 2.12 seconds.

Hence the space time between two successivevehicles at 50 km/h is:

Space Time = Headway time - Occupancy Time= (3600/1700)-(13.5/13.9) = 1.2

seconds

To ensure that the headway time setting will beappropriate for flows of 80% or more of thesaturation flow a calibration factor of 1.25 is used.

The result is divided by the number of normalactive lanes associated with the timer eg for a 3lane approach (2 normally active and one parking)the setting will be:

(1.2 x 1.25)/2 = 0.75 seconds.

Note where there is a shared right turn/throughlane in conjunction with a right turn phase, aspecial headway setting of 0.1 second or as smallas possible is used in conjunction with arecommended 11m presence loop.

18.16.3.8 Waste Timer

The purpose of the waste timer is to accumulatethe amount of wasted time by summing up theexcess of actual headway over the headway timesetting during the controller rest period. The phasewill be terminated when this sum exceeds a limitset by the waste timer.

Typical settings are 10% of maximum green timewith minimum setting - 4 seconds and maximumsetting - 10 seconds.

It is recommended that the waste timer bedisabled for main road movements at isolatedsites in areas where the speed limit is over 60km/h.

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18.16.3.9 Maximum Timer

The purpose of the maximum timer is to controlthe maximum green time available to each phasewhen opposing demands exist and when thecontroller is operating in isolated mode.

The maximum green time is additional to the“minimum” and “variable initial” green time.

The maximum green time setting should besufficient to clear the longest standing queueformed during the red period while theintersection is not over-saturated.

For the first selection it is advisable to select alonger maximum green time since the gap,headway and waste timers should reduce thegreen time if necessary. Calculated phase times asprovided from SIDRA should only be used as aguide to maximum times only.

18.16.4 Pedestrian Times

18.16.4.1 Pedestrian Delay Period

The purpose of the pedestrian delay period is toprovide a delay between the push button actuationand the introduction of the pedestrian feature.This helps form pedestrian “platoons” andtherefore avoid possible unnecessary cycling.

Typical settings are between 5 - 10 seconds.

18.16.4.2 Pedestrian Walk Period

The purpose of the pedestrian walk period is to setthe length of time for the green walk display.

Typical setting is W/2.4 seconds where W is thewidth of the crossing with a minimum of 6seconds.

An additional 2 seconds is allowed for each rankof pedestrians waiting.

Extra time may be allowed for:

• schools;

• rail stations;

• to allow crossing of wide roads (beyondmedians) in one movement;

• elderly, infirm or visually handicappedpedestrians.

18.16.4.3 Pedestrian ClearancePeriods

The purpose of the pedestrian clearance periods isto determine the duration during which a flashingred (DON'T WALK) symbol is displayed.


Total Clearance Period = length of crossing (m) /1.2 (m/s)

Clearance 2 = yellow periodClearance 1 = total clearance period -

clearance 2

The following factors should be considered forvariation of this guideline:

• extremely long crossings in which case provideclearance to the nearest refuge;

• special pedestrian characteristics eg aged,blind, physically handicapped where speed of1.2 m/s should be reduced.

18.16.5 Presence Timer

The purpose of the presence timer is to set aperiod for which a detector must be occupiedbefore a demand is registered.


• 2-5 seconds for 11m turning detector loops (3loop configuration);

• 3 seconds for left turn detector on overlappedmovements.

References

Queensland Department of Main Roads (1995):Manual of Uniform Traffic Control Devices.

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Queensland Department of Main Roads:Guidelines on the Use of Portable Traffic Signals.

Queensland Department of Main Roads: StandardDrawings. Roads.

Roads and Traffic Authority (NSW): TrafficSignal Practice - Design.

Austroads (1988a): Guide to Traffic EngineeringPractice - Part 6. Roundabouts.

Austroads (1988b): Guide to Traffic EngineeringPractice - Part 7. Traffic Signals.

Austroads (1999): Guide to Traffic EngineeringPractice - Part 14. Bicycles.

Australian Standard AS1742 Part 14 - Manual ofUniform Traffic Control Devices. Traffic Signals.

Australian Standard AS2276.1 - Cables for TrafficSignal Installations. Multicore power cables.

Australian Standard AS/NZS2276.2 - Cables forTraffic Signal Installations. Feeder cables forvehicle detectors.

Australian Standard AS2276.3 - Cables for TrafficSignal Installations. Loop cable for vehicledetectors.

Australian Standard AS/NZS 3000 :2000 - WiringRules.

Queensland Transport: Bicycle Notes.

Relationship to OtherChapters

• Close relationship to Chapter 13;

• Chapter 17 provides the details for lighting – anessential part of signalised intersections;

• Cross section details are included in Chapter 7;

• Traffic data requirements are discussed inChapter 5.

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Documents

Traffic Signals - tmr.qld.gov.au/media/busind/techstdpubs/Road planning and... · References Style changed as per the other chapters. ... “Manual of Uniform Traffic Control Devices