New Chapter IIIChapter III TRANSPORTATION SYSTEM ANALYSIS · 2013. 3. 6. · Chapter IIIChapter III TRANSPORTATION SYSTEM ANALYSIS Tewodros N. [email protected]. Lecture Overview

Chapter IIIChapter III TRANSPORTATION SYSTEM

ANALYSIS

Tewodros N.www.tnigatu.wordpress.com

[email protected]

Lecture Overview Traffic engineering studies

Spot speed studies Volume studies Travel time and delay studies Parking studies

F d l i i l f ffi fl Fundamental principles of traffic flow Traffic flow elements Flow-density relationships Fundamental diagram of traffic flow g Mathematical relationships describing traffic flow Shock waves in traffic streams Gap and gap acceptance

Queuing Analysis Queuing Patterns Queuing models Q g

Transport Engineering School of Civil andTewodros N. Environmental Engineering

Traffic Engineering Studies • To reduce the negative impact of highways,

it is necessary to adequately collectit is necessary to adequately collect information that describes the extent of the problems and identifies their locations. pSuch information is usually collected by organizing and conducting traffic surveys and studies.

Spot speed studies Volume studiesVolume studies Travel time and delay studies Parking studies


Traffic Engineering Studies Cont…

Traffic studies may be grouped into three i t imain categories• Inventories:- provide a list or graphic display of existing

information such as street widths parking spaces transitinformation, such as street widths, parking spaces, transit routes, traffic regulations, and so forth.

• Administrative studies:- use existing engineering records, available in government agencies and departments.

– Used to prepare an inventory of the relevant data.

• Dynamic studies: collection of data under operational• Dynamic studies:- collection of data under operational conditions and include studies of speed, traffic volume, travel time and delay, parking, and accidents.


Spot speed studies p pConducted to estimate the distribution of speeds of

vehicles in a stream of traffic at a particular location on a hi hhighway.

Uses to:-Establish speed zonespDetermine whether complaints about speeding are validEstablish passing and no-passing zonesDesign geometric alignmentDesign geometric alignment Analyze accident data Evaluate the effects of physical improvements D t i th ff t f d f t dDetermine the effects of speed enforcement programs and

speed control measures Determine speed trends


Spot speed studies Cont…

Locations for Spot Speed Studies:- Depend on the anticipated use of the resultsanticipated use of the results 1. Locations that represent different traffic conditions on a high a or high a s are sed for b sic d t collectiona highway or highways are used for basic data collection. 2. Mid-blocks of urban highways and straight, level sections of rural highways are sites for speed trend analysessections of rural highways are sites for speed trend analyses. 3. Any location may be used for the solution of a specific traffic engineering problemtraffic engineering problem.


Spot speed studies Cont…• Definitions of values that are used to describe speed

characteristics: Average speed

Median speed M d l d Modal speed The ith-percentile spot speed Pace Standard deviation of speeds


Spot speed studies Cont…Sample Size for Spot Speed Studies • The minimum sample size depends on the precision level desired. • The confidence level is commonly given in terms of the level of significance (α),

where α= (100 confidence level)where α= (100 - confidence level). • Normal distribution have been used to develop an equation relating the sample size

to the number of standard variations corresponding to a particular confidence level, the limits of tolerable error, and the standard deviation.

• Where: N= minimum sample size; Z = number of standard deviations corresponding to the required confidence level 1.96 for 95 percent confidence level; σ = standard deviation (mph); d = limit of acceptable error in the speed estimate (mph)( p ) p p ( p )


Example• Determine the minimum sample size required for a

spot peed study on a rural highway if the confidence level for the study is 95 0 percent and the tolerancelevel for the study is 95.0 percent and the tolerance 1.0mph Assume a standard deviation of + 5.30mph.

SolutionSolve for N:-Solve for N:

N = [(1.96 x 5.3)/1]2=108

The sample size should therefore be at least 108The sample size should therefore be at least 108


Spot speed studies Cont…

Methods for Conducting Spot Speed Studies1 Th th t d d t t1. Those that use road detectors, 2. Those that use Doppler principle meters (radar type), and3. Those that use the principles of electronics


Road Detectors Classified into two general categories: pneumatic road tubes (air

impulse) and induction loops (electric resonance circuit). Devices can be used to collect data on speeds at the same

time as volume data are being collected. Th d f h d i h h The advantage of the detector meters is that human errors

are considerably reduced. The disadvantages are that The disadvantages are that

(1) these devices tend to be rather expensive, and (2) when pneumatic tubes are used, they are rather ( ) p , yconspicuous and may, therefore, affect driver behavior, resulting in a distortion of the speed distribution.


Road Detectors Cont…

pneumatic road tubes


Road Detectors Cont…

induction loops


Doppler-Principle Meters Work on the principle that when a signal is

transmitted onto a moving vehicle, the change in f b h i d i l d hfrequency between the transmitted signal and the reflected signal is proportional to the speed of the moving vehicle. g

The difference between the frequency of the transmitted signal and that of the reflected signal is

d b h i d h dmeasured by the equipment, and then converted to speed in mph.

The value of the speed recorded depends on thatThe value of the speed recorded depends on that angle.


Doppler-Principle Meters Cont…

RADAR/LIDAR Technology


Electronic-Principle Detectors The presence of vehicles is detected through electronic

means, and information on these vehicles is obtained, , ,from which traffic characteristics such as speed, volume, queues, and headways are computed.

Not necessary to physically install loops or any other type of detector on the road.

Electronics is video image processing, sometimes referred to as a machine-vision system.


Electronic-Principle Detectors Cont…

Autoscope Systems


ExampleFor the data shown below determine

Arithmetic mean d d dStandard deviation Median speed Pace Modal speed


Volume studies Are conducted to collect data on the number of vehicles

and/or pedestrians that pass a point on a highway facility d ring a specified time periodduring a specified time period.

The data collected may also be put into subclasses which may include directional movement, occupancy rates, vehicle classification, and pedestrian age.

Volume characteristics Average Annual Daily Traffic (AADT)Average Annual Daily Traffic (AADT) Average Daily Traffic (ADT) Peak Hour Volume (PHV) Vehicle Classification (VC)Vehicle Miles of Travel (VMT)


Volume studies Cont… Methods of Conducting Volume Counts Manual Method

Disadvantages of the manual count method are that(1) it is labor-intensive and can therefore be expensive, (2) it is subject to the limitations of human factors, and (3) it cannot be used for long periods of counting.

A i M h dAutomatic Method Involves the laying of surface detectors (such as pneumatic road tubes) or subsurface detectors (such as magnetic orroad tubes) or subsurface detectors (such as magnetic or electric contact devices) on the road.


Volume studies Cont…

Jamar Technologies


Volume studies Cont… Types of Volume Counts:- Depends on the anticipated use of the data to be

collected. C d C t Wh i f ti i i d hi lCordon Counts :- When information is required on vehicle

accumulation within an area, such as the central business district (CBD) of a city, particularly during a specific time, a cordon count is undertakenundertaken.

Screen Line Counts:- In screen line counts, the study area is divided into large sections by running imaginary lines known as screen lines, across it. Traffic counts are then taken at each point where a roadacross it. Traffic counts are then taken at each point where a road crosses the screen line.

Intersection Counts:- Intersection counts are taken to determine vehicle classifications, through movements and turning movements at , g gintersections.

Pedestrian Volume Counts Periodic Volume CountsPeriodic Volume Counts


Volume studies Cont… f b f Determination of Number of Count Stations

When the sample size is less than 30 and the selection of counting stations is random, a distribution known as the student's t distribution may be used to determine the sample size for each class of highway links. p g y

The student's t distribution is unbounded, with a mean of zero, and The degrees of freedom (v) is a function of the sample size; v= N -1 The variance of the student's t distribution is ν/(ν- 2) The variance of the student s t distribution is ν/(ν 2) Variance that depends on the scale parameter, commonly referred to as the degrees of freedom

(v).

Where:- n = minimum number of count locations required; t = value of the student's t distribution with (1 α/2) confidence level (N 1 degrees of freedom); Nstudent s t distribution with (1 -α/2) confidence level (N - 1 degrees of freedom); N = total number of links (population) from which a sample is to be selected α= significance level; S = estimate of the spatial standard deviation of the link volumes; d= allowable range of error


ExampleTo determine a representative value for the ADT on 100 highway links that haveTo determine a representative value for the ADT on 100 highway links that have similar volume characteristics, it was decided to collect 24-hr volume counts on sample of these link. Estimates of the mean and standard deviation of the link volumes for the type of the highway in which these links are located are 32,500 and 5 500 respectively Determine the minimum number of the stations at which5,500, respectively. Determine the minimum number of the stations at which volumes counts should be taken if a 95-10 precision level is required.

Solution


Volume studies Cont… Expansion Factors from Continuous Count

StationsStat o sHourly expansion factors (HEFs)

Daily expansion factors (DEFs)

M hl i f (MEF ) dMonthly expansion factors (MEFs) are computed as


ExampleA traffic engineer urgently needs to determine the AADT on a rural primary road that has volume distribution characteristics shown in tables shown below. She collected the data shown below on Tuesday during the month of May. Determine the AADT f th dAADT of the road.


Travel time and delay studies Determines the amount of time required to travel from one point to another on Determines the amount of time required to travel from one point to another on

a given route. Information may also be collected on the locations, durations, and causes of

delays.y Applications of Travel Time and Delay Data

Determination of the efficiency of a route with respect to its ability to carry traffic

Id ifi i f l i i h l i l hi h d l d h f h Identification of locations with relatively high delays and the causes for those delays

Performance of before-and-after studies to evaluate the effectiveness of traffic operation improvements p p

Determination of relative efficiency of a route by developing sufficiency ratings or congestion indices

Determination of travel times on specific links for use in trip assignment models C il i f l i d h b d i d di l h Compilation of travel time data that may be used in trend studies to evaluate the

changes in efficiency and level of service with time Performance of economic studies in the evaluation of traffic operation

alternatives that reduce travel time.


Travel time and delay studies Definition of Terms Related to Time and Delay Studies

• Travel time:- is the time taken by a vehicle to traverse a given section of a highway

• Running time:- is the time a vehicle is actually in motion while traversing a give section of a highway.

• Delay:- is the time lost by a vehicle due to causes beyond the control of the driverthe driver.

• Operational delay:- is that part of the delay caused by the impedance of other traffic

• Stopped-time delay :- is that part of the delay during which the vehicle isStopped time delay : is that part of the delay during which the vehicle is at rest

• Fixed delay:- is that part of the delay caused by control devices such as traffic signals.

• Travel-time delay :- is the difference between the actual travel time and the time that will be obtained by assuming that a vehicle traverses the study section at an average speed equal to that for an uncontested traffic flow on the section being studied. g


Travel time and delay studies

M th d f C d ti T l TiMethods for Conducting Travel Time and Delay StudiesyThose using a test vehicle andTh t r iri t t hi lThose not requiring a test vehicle.


Those using a test vehicle Floating-Car Technique. In this method, the test car is driven by an observer along the

test section so that the test car "floats" with the traffic. This is repeated, and the average time is as the travel time.

The minimum number of test runs

Average Speed Technique This technique involves driving the test car along the length of Average-Speed Technique. This technique involves driving the test car along the length of the test section at a speed that, in the opinion of the driver, is the average speed of traffic stream.

Determines the amount of time required to travel from one point to another on a igiven route.

Information may also be collected on the locations, durations, and causes of delays. Applications of Travel Time and Delay Data


Those using a test vehicle Cont… Moving-Vehicle Technique. In this technique, the observer makes a round trip on a test

section like the one shown in below, where it is assumed that the road runs east-west.

The time it takes to travel from X-X to Y-Y (Te), in minutes ( ) The time it takes to travel from Y-Y to X-X (Tw), in minutes The number of vehicles traveling west in the opposite lane while the test car is

traveling east (Ne) Th b f hi l h k h hil i i li f Y Y The number of vehicles that overtake the test car while it is traveling from Y-Y to

X-X, that is, traveling in the westbound direction (Ow) The number of vehicles that the test car passes while it is traveling from Y-Y to

X-X, that is, traveling in the westbound direction (Pw) g ( ) The volume (Vw) in the westbound direction can then be obtained from the

expression


Methods Not Requiring a Test Vehicleq g

License-Plate Observations. The license-plate method prequires that observers be positioned at the beginning and end of the test section. Each observer records the last three or four digits of the license plate of each carlast three or four digits of the license plate of each car that passes, together with the time at which the car passes.

Interviews. The interviewing method is carried out by obtaining information from people who drive on theobtaining information from people who drive on the study site regarding their travel times, their experience of delays, and so forth.


Parking studies

• On-Street Parking Facilities:- These are also known gas curb facilities. Parking bays are provided alongside the curb on one or both sides of the streetstreet.

• Off-Street Parking Facilities:- These facilities may be privately or publicly owned; they include surfaceprivately or publicly owned; they include surface lots and garages.


Parking studies Cont… • D fi iti f P rki T r• Definitions of Parking Terms

• A space-hour:- is a unit of parking that defines the use of a single parking space for a period of 1 hr. P ki l i h l b f hi l h k i d• Parking volume:- is the total number of vehicles that park in a study area during a specific length of time, usually a day.

• Parking accumulation:- is the number of parked vehicles in a study area at any specified time These data can be plotted as a curve of parkingat any specified time. These data can be plotted as a curve of parking accumulation against time, which shows the variation of the parking accumulation during the day.

• The parking load:- is the area under the accumulation curve betweenThe parking load: is the area under the accumulation curve between two specific times.

• Parking duration :- is the length of time a vehicle is parked at a parking bay. y

• Parking turnover:- is the rate of use of a parking space. It is obtained by dividing the parking volume for a specified period by the number of parking spaces.


Parking studies Cont…

On- StreetOn Street Parking


Parking studies Cont…

Off- StreetOff Street Parking


Tha k Y !Thank You!Y

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New Chapter IIIChapter III TRANSPORTATION SYSTEM ANALYSIS · 2013. 3. 6. · Chapter IIIChapter III TRANSPORTATION SYSTEM ANALYSIS Tewodros N. [email protected]. Lecture Overview