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Tra nsit C a p a c ity a nd Q ua lity of Se rvic e M a nua l2ndEd ition

PART 4BUS TRANSIT CAPACITY

CONTENTS

CHAPTER 1. BUS CAPACITY FUNDAMENTALS..................................................... 4-1

Overview .......................................................................................................................... 4-1

Capacity Calculation Process.........................................................................................4-1

Loading Areas..............................................................................................................4-2

Bus Stops.......................................................................................................................4-2

Bus Facilities.................................................................................................................4-3

Person Capacity ...........................................................................................................4-3

Loading Area Bus Capacity ...........................................................................................4-3

Dwell Time ...................................................................................................................4-3

Clearance Time ............................................................................................................4-7

Dwell Time Variability................................................................................................4-8

Traffic Signal Timing.................................................................................................4-10

Calculation Procedure............................................................................................... 4-10

Bus Stop Vehicle Capacity............................................................................................4-11

Design and Location Considerations......................................................................4-11

Bus Stop Effectiveness...............................................................................................4-12

Calculation Procedure............................................................................................... 4-15

Bus Facility Concepts .................................................................................................... 4-16

Person Capacity .............................................................................................................4-16

Loading Diversity......................................................................................................4-16

Operator Policy ..........................................................................................................4-17

CHAPTER 2. BUS PREFERENTIAL TREATMENTS................................................ 4-19

Introduction ................................................................................................................... 4-19

Bus Preferential Treatment Uses ............................................................................. 4-19

Person Delay Concepts ............................................................................................. 4-20

Busways and Freeway HOV Lanes.............................................................................4-20

Operational Overview .............................................................................................. 4-21

HOV Lanes ................................................................................................................. 4-23

Freeway Ramp Queue Bypasses.............................................................................. 4-23

Arterial Street Bus Lanes .............................................................................................. 4-24

Traffic Signal Priority....................................................................................................4-25

Overview .................................................................................................................... 4-25

Notes on Application ................................................................................................ 4-26

Site-Specific Priority Treatments ................................................................................. 4-27

Queue Jumps.............................................................................................................. 4-27

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CHAPTER 6. MIXED TRAFFIC..................................................................................... 4-57

Introduction ................................................................................................................... 4-57

Types of Bus Operations............................................................................................... 4-57

Bus Capacity...................................................................................................................4-57

Bus Speeds......................................................................................................................4-59

CHAPTER 7. DEMAND-RESPONSIVE TRANSPORTATION.............................. 4-61

Introduction ................................................................................................................... 4-61

Service Characteristics .................................................................................................. 4-61

Vehicle Types ................................................................................................................. 4-62

DRT Capacity ................................................................................................................. 4-62

Capacity Factors.........................................................................................................4-62

Capacity Calculation Procedure .............................................................................. 4-63

CHAPTER 8. REFERENCES........................................................................................... 4-65

CHAPTER 9. EXAMPLE PROBLEMS ..........................................................................4-69

APPENDIX A: EXHIBITS IN METRIC UNITS .......................................................... 4-91

APPENDIX B: DWELL TIME DATA COLLECTION PROCEDURE ..................... 4-93

APPENDIX C: BUS EFFECTS ON ADJACENT LANE VEHICLE CAPACITY .... 4-97

APPENDIX D: PLANNING-LEVEL CAPACITY GRAPHS..................................... 4-99

APPENDIX E: EFFECTS OF BUS BUNCHING ON PERSON CAPACITY......... 4-109

LIST OF EXHIBITS

Exhibit 4-1 Bus Loading Areas, Stops, and Facilities ...............................................4-2

Exhibit 4-2 Passenger Service Times with Single-Channel PassengerMovement .................................................................................................. 4-5

Exhibit 4-3 Passenger Service Times with Multiple-Channel PassengerMovement .................................................................................................. 4-6

Exhibit 4-4 On-Line and Off-Line Loading Areas ....................................................4-7

Exhibit 4-5 Average Bus Re-Entry Delay (Random Vehicle Arrivals) ................... 4-7

Exhibit 4-6 Values of ZAssociated with Given Failure Rates.................................4-9

Exhibit 4-7 Illustrative Relationships Between Failure Rate, Operating Margin,and Loading Area Bus Capacity ............................................................. 4-9

Exhibit 4-8 Estimated Maximum Capacity of Loading Areas (bus/h) ................ 4-11

Exhibit 4-9 On-Street Bus Stop Locations ................................................................4-11

Exhibit 4-10 On-Street Bus Stop Location Comparison ........................................... 4-13

Exhibit 4-11 Bus Stop Design Types ...........................................................................4-13

Exhibit 4-12 Efficiency of Multiple Linear Loading Areas at Bus Stops................ 4-14

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Tra nsit Ca p a c ity a nd Q ua lity of Se rvic e M a nua l2ndEd ition

Exhibit 4-13 Relative Contributions of Dwell Time,g/CRatio, and Number ofLoading Areas to Bus Stop Capacity ....................................................4-15

Exhibit 4-14 Estimated Maximum Capacity of On-Line Linear Bus Stops............4-15

Exhibit 4-15 Capacity Factors for Exclusive Bus Lanes............................................ 4-16

Exhibit 4-16 Person Capacity Factors .........................................................................4-17

Exhibit 4-17 Characteristics of Common Bus Transit VehiclesUnited Statesand Canada .............................................................................................. 4-18

Exhibit 4-18 Operating Characteristics of Selected North American Buswaysand Freeway HOV Facilities..................................................................4-21

Exhibit 4-19 Median Bus Lane Examples................................................................... 4-22

Exhibit 4-20 Bus Tunnel Examples ............................................................................. 4-23

Exhibit 4-21 Houston HOV Lane Examples ..............................................................4-23

Exhibit 4-22 Freeway Ramp Queue Bypasses ........................................................... 4-24

Exhibit 4-23 Sources of Delay for Buses Operating in Mixed Traffic atIntersections............................................................................................. 4-24

Exhibit 4-24 Bus Lane Development via Parking Restrictions................................ 4-25

Exhibit 4-25 Bus Signal Priority Systems ...................................................................4-26

Exhibit 4-26 Bus Signal Priority ConceptRed Truncation and GreenExtension .................................................................................................. 4-27

Exhibit 4-27 Reported Benefits Associated with Transit Signal Priority ...............4-27

Exhibit 4-28 Bus Queue Jumps....................................................................................4-28

Exhibit 4-29 Boarding Islands......................................................................................4-29

Exhibit 4-30 Curb Extensions ......................................................................................4-30

Exhibit 4-31 Yield-to-Bus Law Notifications .............................................................4-30

Exhibit 4-32 Example Skip-Stop Pattern and Signing ..............................................4-33

Exhibit 4-33 Bus Preferential Treatments Comparison............................................ 4-34

Exhibit 4-34 Typical Busway and HOV Lane Minimum Operating Thresholds..4-35

Exhibit 4-35 General Planning Guidelines for Bus Preferential Treatments:Uninterrupted Flow Facilities................................................................4-36

Exhibit 4-36 General Planning Guidelines on the Effects of Bus PreferentialTreatments: Uninterrupted Flow Facilities..........................................4-36

Exhibit 4-37 General Planning Guidelines for Bus Preferential Treatments:Urban Streets ...........................................................................................4-37

Exhibit 4-38 General Planning Guidelines for Bus Preferential Treatments:Intersections............................................................................................. 4-38

Exhibit 4-39 General Planning Guidelines on the Effects of Bus PreferentialTreatments: Intersections .......................................................................4-39

Exhibit 4-40 Planning-Level Bus Lane Service Volumes ......................................... 4-39

Exhibit 4-41 Maximum Bus Passenger Service Volumes for Planning Purposes. 4-40

Exhibit 4-42 Illustrative Downtown Busway Capacities ......................................... 4-41

Exhibit 4-43 Factors Influencing Bus Capacity and Speed ...................................... 4-42

Exhibit 4-44 Typical Grade-Separated Busway Design Features ...........................4-43

Exhibit 4-45 Illustrative Capacity Constraints After Exclusive Busway Section .. 4-44

Exhibit 4-46 Freeway HOV Lane with Off-Line Stop (Seattle) ...............................4-46Contents Page 4-iv Part 4/BUS TRANSIT CAPACITY


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Exhibit 4-47 Estimated Average Speeds of Buses Operating on Busways andExclusive Freeway HOV Lanes (mph).................................................4-46

Exhibit 4-48 Exclusive Bus Lane Types......................................................................4-47

Exhibit 4-49 Examples of Auto Turning Conflicts with Buses................................ 4-48

Exhibit 4-50 Right-Turn Vehicle Capacities for Planning Applications ................ 4-48

Exhibit 4-51 Bus Stop Location Factors,fl ..................................................................4-49Exhibit 4-52 Typical Values of Adjustment Factor,fk, for Availability of Adjacent

Lanes.........................................................................................................4-50

Exhibit 4-53 Values of Adjustment Factor,fk, for Type 2 Bus Lanes with AlternateTwo-Block Skip-Stops.............................................................................4-50

Exhibit 4-54 Illustrative Bus Lane Vehicle Capacity: Non-Skip-Stop Operation.. 4-51

Exhibit 4-55 Illustrative Bus Lane Vehicle Capacity: Skip-Stop Operation........... 4-52

Exhibit 4-56 Estimated Base Bus Running Time, tr(min/mi) .................................4-53

Exhibit 4-57 Estimated Base Bus Running Time Losses, tl(min/mi)..................... 4-53

Exhibit 4-58 Illustrative Skip-Stop Speed Adjustment Effects ................................4-54

Exhibit 4-59 Bus-Bus Interference Factor,fb............................................................... 4-55Exhibit 4-60 Illustrative Bus-Bus Interference Factor Effects ..................................4-55

Exhibit 4-61 Types of Mixed Traffic Bus Operations ...............................................4-57

Exhibit 4-62 Illustrative Mixed Traffic Maximum Bus Vehicle Capacity ..............4-58

Exhibit 4-63 Sample Passenger Service Time Data Collection Sheet......................4-94

Exhibit 4-64 Sample Dwell Time Data Collection Sheet .......................................... 4-95

Exhibit 4-65 Bus Stop Capacity with 400 veh/h in Curb Lane and Off-lineStops........................................................................................................ 4-100

Exhibit 4-66 Bus Stop Capacity with 800 veh/h in Curb Lane and Off-lineStops........................................................................................................ 4-101

Exhibit 4-67 Bus Stop Capacity with On-Line Stops ..............................................4-102

Exhibit 4-68 Exclusive Lane Bus Capacity: Near-side Stops, Type 1 Lane.......... 4-103

Exhibit 4-69 Exclusive Lane Bus Capacity: Near-side Stops, Type 2 Lane.......... 4-104

Exhibit 4-70 Exclusive Lane Bus Capacity: Far-side Stops, Type 1 Lane............. 4-105

Exhibit 4-71 Exclusive Lane Bus Capacity: Far-side Stops, Type 2 Lane............. 4-106

Exhibit 4-72 Exclusive Lane Bus Capacity: Type 3 Lane........................................ 4-107

Exhibit 4-73 Mixed Traffic Bus Capacity: Type 1 Lane .......................................... 4-107

Exhibit 4-74 Mixed Traffic Bus Capacity: Type 2 Lane .......................................... 4-108

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CHAPTER 1. BUS CAPACITY FUNDAMENTALS

OVERVIEW

Bus capacity is a complex topic: it deals with the movement of both people andvehicles, depends on the size of the buses used and how often they operate, and

reflects the interaction between passenger traffic concentrations and vehicle flow. Italso depends on the operating policy of the service provider, which normallyspecifies service frequencies and allowable passenger loadings. Ultimately, thecapacities of bus routes, bus lanes, and bus terminals, in terms of persons carried, aregenerally limited by (1) the ability of stops or loading areas to pick up and dischargepassengers, (2) the number of vehicles operated, and (3) the distribution of boardingsand alightings along a route.

Part 4 of the Transit Capacity and Quality of Service Manual (TCQSM) presentsmethods for calculating bus capacity and speed for a variety of facility and operatingtypes.

Organization of Part 4.

Chapter 1introduces the basic factors that determine bus capacity.

Chapter 2 discusses transit preferential treatments and operating measuresthat influence bus performance.

Chapter 3 presents planning applications that can be used to determine theeffects of transit priority measures.

Chapters 4 through 6discuss busways, freeway HOV lanes, arterial street buslanes, and operations in mixed traffic.

Chapter 7presents issues related to demand-responsive transportation.

Chapter 8contains the references used within this part of the manual.

Chapter 9presents example problems that apply Part 4 procedures to realworld situations.

Appendix A provides substitute exhibits in metric units for Part 4 exhibits

that use U.S. customary units.

Exhibits also appearing in Appendix Aare indicated by a margin note such

as this.

Appendix Bprovides a standardized procedure for collecting bus dwell timedata in the field.

Appendix Cpresents information of interest to users of the Highway CapacityManualon determining bus effects on adjacent lane vehicle capacity.

Appendix Dprovides planning-level graphs applying the bus stop and lanecapacity procedures presented in this part of the TCQSM.

Appendix Ediscusses the effects of bus bunching on bus capacity.

CAPACITY CALCULATION PROCESS

Bus capacity is calculated for three key locations:Loading Area Capacity

Bus Stop Capacity

Bus Facility Capacity

Loading Area Capacity

Bus Stop Capacity

Bus Facility Capacity

1. Bus loading areas (berths)are curbside spaces where a single bus can stop toload and unload passengers.

2. Bus stops are formed from one or more loading areas, depending on howmany buses can use the stop simultaneously.

3. Bus facilitiesare roadways used by buses and may contain multiple bus stopsalong their length.

Bus stop capacity is dependent on the individual capacities of the loading areasthat form the bus stop. Similarly, a bus facilitys capacity will be constrained by the

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capacity of the critical stop along the facility, which is typically the stop with thehighest passenger volumes and the longest dwell time. Exhibit 4-1 shows therelationships of loading areas, stops, and facilities.

LL

SF

L = loading area, S = bus stop, F = bus facility

Bus Bus

LL

S

LLLL

SF

L = loading area, S = bus stop, F = bus facility

Bus Bus

LLLL

S

Exhibit 4-1Bus Loading Areas, Stops,and Facilities

Loading Areas

The bus capacity of a loading area is dependent on the following factors:

Dwell timethe average amount of time a bus is stopped at the curb to servepassenger movements, including the time required to open and close thedoors;

Dwell time plus clearance time

equals the average time agiven bus occupies a loadingarea.

Clearance timethe minimum time required for one bus to accelerate out ofand clear the loading area and the next bus to pull into the loading area,including any time spent waiting for a gap in traffic;

Dwell time variabilitythe consistency (or lack thereof) of dwell times amongbuses using the loading area; and

Dwell time variability andfailure rate account for longer-than-average dwells so thatone bus typically does notdelay the one behind it.

Failure ratethe probability that one bus will arrive at a loading area, only tofind another bus already occupying it.

The combination of dwell time and clearance time gives the average amount oftime an individual bus occupies the loading area. The combination of dwell time

variability and a design failure rate provides an additional margin of time to ensurethat most buses will be able to immediately use the loading area upon arriving.Adding these two combinations together produces the minimum headway betweenbuses required to avoid interference between buses. Dividing this headway into thenumber of seconds in an hour gives the number of buses per hour that can use thestopthe loading area capacity.

Bus Stops

The bus capacity of a bus stop is based on the following:

Number of loading areas providedtwo loading areas will be able toaccommodate more buses than a single loading area, but not necessarily twotimes as many;

Loading area designhow the loading areas are designed determines howmuch extra capacity each additional loading area will provide; and

Traffic controltraffic signals may constrain the number of buses that canleave (or enter) a stop during a given period of time. If a bus is ready to leavea stop, but a red traffic signal prevents it from doing so, the bus will occupythe stop longer, and the bus stop capacity will be lower as a result.

Traffic signals limit when busesare able to enter or exit stopslocated nearby, and thus theyconstrain capacity.

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Bus Facilities

The capacity of an on-street bus facility is based on the following:

Critical bus stop capacitythe bus stop with the lowest capacity along thefacility will constrain how many buses can pass through it. This bus stop isusually the stop with the longest dwell time, but heavy right-turning trafficvolumes at near-side bus stops or a traffic signal that provides only a shortperiod of green time for the bus facility can also be constraints.

The bus stop with the lowestcapacitythe critical stopconstrains facility capacity.

Operational proceduresbus route design that spreads bus stopping activityover a group of stops (skip-stops), rather than having all buses stop at thesame set of stops, can greatly increase the capacity of an on-street facility.

The capacity of freeway high-occupancy vehicle (HOV) lanes, where buses donot stop along the lanes, is generally not an issue. The number of buses that can usean HOV lane will be constrained by the capacity of a bus terminal or on-street facilitybefore or after the lane. When an HOV lane is shared with a large number of othervehicles, the Highway Capacity Manualcan be used to determine the total number ofvehicles or passenger car equivalents that can use the lane before it becomescongested.

The number of buses that can usenon-stop facilities such as HOV lanesis usually constrained by on-streetfacilities or off-street terminalselsewhere.

Person CapacityThe maximum number of people that can be transported through the facility

during a given time period can be determined from the following:

Bus capacity of the facilitythe number of buses that can use the facilityduring a given period of time;

Once the maximum number of busesthat can use a facility in a given timeis known, the number of people thatcan be transported by those busescan be readily calculated.

Maximum schedule load of the buses using the facilitythe maximum number ofpeople aboard each bus using the facility; and

Passenger demand characteristicsnot all of the offered capacity will be used,as passengers will arrive at uneven rates, and service should be designed soas not to pass up any passengers. A peak hour factor is used to reduce thetheoretical capacity (i.e., the number of buses per hour multiplied by the

number of people per bus) to a person capacity that can be achieved on asustained basis day after day.

LOADING AREA BUS CAPACITY

Dwell Time

The capacity of individual loading areas is fundamental to determining thecapacities of bus stops and facilities. In turn, the average dwell times at loading areasare fundamental to determining the capacities of those areas.

Dwell time is the most importantcomponent of loading area, bus stop,and facility capacity.

Dwell times may be governed by boarding demand (e.g., in the p.m. peak periodwhen relatively empty buses arrive at a heavily used stop), by alighting demand(e.g., in the a.m. peak period at the same location), or by total interchangingpassenger demand (e.g., at a major transfer point). In all cases, dwell time is

proportional to the boarding and/or alighting volumes and the amount of timerequired to serve each passenger.

There are five main factors that influence dwell time. Two of these relate topassenger demand, while the other three relate to passenger service times:

Passenger Demand and Loading. The number of people passing through thehighest-volumedoor is a key factor in how long it will take for all passengersto be served. The proportion of alighting to boarding passengers through thebusiest door also affects how long it takes all passenger movements to occur.

The highest-volume door generallydetermines how long it takes to serveall boarding or alighting passengers.



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Bus Stop Spacing.The smaller the number of stops, the greater the number ofpassengers boarding at a given stop. A balance is required betweenproviding too few stops, each with relatively high dwell times and relativelylong passenger walk times, and providing too many stops (which reduceoverall travel speeds due to the time lost in accelerating, decelerating, andpossibly waiting for a traffic signal every time a stop is made).

Fare Payment Procedures.The average time to pay a fare is a major influenceon the time required to serve each boarding passenger. Some types of fare-payment procedures allow passengers to board through more than one doorat busy stops, thus allowing all passengers to be served more quickly.

Fare payment method stronglyinfluences dwell time.

Passengers stopping to askbus operators questions alsoimpacts dwell time, particularlyfor tourist-oriented services.Providing information at stopsabout how to ride and placesto go can help.

Vehicle Types.Having to ascend or descend steps while getting on and off thebus increases the amount of time required to serve each passenger.

In-Vehicle Circulation.When standees are present on a bus, it takes more timefor boarding passengers to clear the farebox area, as other passengers mustmove to the back of the bus.

Dwell time can also be affected by the time required for wheelchair loading andsecurement and for bicyclists to use bus-mounted bicycle racks. However, unlessthese activities occur regularly at a given stop, they can be treated as random events

that are addressed by dwell time variability (i.e., a wheelchair loading will result in alonger-than-average dwell time when it occurs, but these events happen rarely).

Wheelchair and bicycleboarding times may also needto be considered whencalculating dwell time, but are

accounted for by dwell timevariability when they occurinfrequently.

Combinations of these factors can substantially reduce dwell times. In the late1990s, Denvers 16th Street Mall shuttle operation maintained 75-second peakheadways with scheduled 12.5-second dwell times, despite high peak passenger

loads on its 70-passenger buses.1This was accomplished through a combination offare-free service, few seats (passenger travel distances are short), low-floor buses, andthree double-stream doors on the buses.

A double-stream (two-channel)door is wide enough to allowtwo passengers to use it at thesame time.

Estimating Dwell Time

Three methods can be used to estimate bus dwell times:

1. Field measurementsbest for evaluating an existing bus route;

2. Default valuessuitable for future planning when reliable estimates of futurepassenger boarding and alighting volumes are unavailable; and

3. Calculationsuitable for estimating dwell times when passenger boardingand alighting counts or estimates are available.

Method 1: Field Measurements

The most accurate way to determine bus dwell times at a stop is to measure themdirectly. An average (mean) dwell time and its standard deviation can be determinedfrom a series of observations. Appendix Bpresents a standardized methodology formeasuring bus dwell times in the field.

Best for evaluating existingbus routes. See Appendix B fordetails.

Method 2: Default Values

If field data or passenger counts are unavailable for a bus stop, the followingrepresentative values can be used to estimate dwell time at the critical (busiest) stop:60 seconds at a downtown stop, transit center, major on-line transfer point, or majorpark-and-ride stop; 30 seconds at a major outlying stop; and 15 seconds at a typicaloutlying stop.(R26)

Suitable for future planningwhen reliable passengerestimates are unavailable.

1 Denvers Regional Transit District (RTD) began using 116-passenger hybrid electric/compressed natural gas buses in 1999 to accommodate growing passenger demand for this service.


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Method 3: Calculation

This method requires that passenger counts or estimates be available,categorized by the number of boarding and alighting passengers.

Suitable when passenger counts orestimates are available.

Step 1: Obtain hourly passenger volume estimates.These estimates are required onlyfor the highest-volume stops. When skip-stop operations are used (see Chapter 2),estimates are needed for the highest-volume stops in each skip-stop sequence.

Step 2: Adjust hourly passenger volumes for peak passenger volumes. Equation 4-1shows the peak hour factor (PHF) calculation method. Typical peak hour factorsrange from 0.60 to 0.95 for transit lines. (R18,R40) In the absence of other information,0.75 may be used as a default PHF for bus service where the schedule is not adjustedto accommodate peaks in demand (e.g., when clock headways are used). Whenheadways are adjusted to serve predictable peaks in demand, a PHF of 0.85 may beused as a default. A PHF close to 1.0 may well indicate system overload(underservicing) and reveal the potential for more service. If buses operate at longerthan 15-minute headways, the denominator of Equation 4-1 should be adjustedappropriately (e.g., 3P20 for 20-minute headways). Equation 4-2 adjusts hourlypassenger volumes to reflect peak-within-the-peak conditions.

Peak hour factors are used (1) todevelop equivalent hourly volumesbased on peak 15-minute demands,and (2) adjust person capacities toreflect variations in passengerdemand over the course of an hour.

15

h

P

P

PHF 4= Equation 4-1

)(4PHF

PP h15 = Equation 4-2

where:PHF = peak hour factor; Peak hour factors range from 0.25

(all passenger demand occurs duringa single 15-minute period in an hour)to 1.00 (demand is constantthroughout the hour).

Ph = passenger volume during the peak hour (p); andP15 = passenger volume during the peak 15 minutes (p).

Step 3: Determine the base passenger service time.Exhibit 4-2 can be used to estimatethese times for typical situations where only one direction of passengers uses a doorat a time and all passengers board through a single door. When passengers mayboard through multiple doors (for example, free shuttles, proof-of-payment or pay-on-exit fare collection, or boarding from a fare-paid area), Exhibit 4-3 can be usedinstead to estimate these times. Note that having two doors available for boardingdoes not halve the average passenger boarding time, although it provides asignificant improvement.

Exhibit 4-2Passenger Service Times withSingle-Channel PassengerMovement

Passenger Service Time (s/p)Situation Observed Range Suggested Default

BOARDING

Pre-payment* 2.25-2.75 2.5Single ticket or token 3.4-3.6 3.5Exact change 3.6-4.3 4.0Swipe or dip card 4.2 4.2Smart card 3.0-3.7 3.5

ALIGHTINGFront door 2.6-3.7 3.3Rear door 1.4-2.7 2.1

Comparing relative service times ofdifferent fare payment methods canbe used to estimate the dwell timeimpacts of changing the paymentmethod.

*includes no fare, bus pass, free transfer, and pay-on-exitAdd 0.5 s/p to boarding times when standees are present.Subtract 0.5 s/p from boarding times and alighting times on low-floor buses.



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Exhibit 4-3Passenger Service Timeswith Multiple-ChannelPassengerMovement(R5,R20,R23,R24)

Available Default Passenger Service Time (s/p)Door Channels Boarding* Front Alighting Rear Alighting

1 2.5 3.3 2.12 1.5 1.8 1.23 1.1 1.5 0.94 0.9 1.1 0.76 0.6 0.7 0.5

*Assumes no on-board fare payment requiredIncrease boarding times by 20% when standees are present. For low-floor buses, reduce boarding times by20%, front alighting times by 15%, and rear alighting times by 25%.

Step 4: Adjust the passenger service times for heavy two-flow through a single doorchannel.When 25 to 50% of the passenger flow through a single door channel is in theopposite direction of the main flow of passengers, increase both the boarding andalighting passenger service times by 20% (0.5 seconds for a single door channel) toaccount for passenger congestion at the door.(R40)

Passenger service timesincrease when significant two-way passenger flow occursthrough a door.

Step 5: Calculate the dwell time. The dwell time is the time required to servepassengers at the busiest door, plus the time required to open and close the doors. Avalue of 2 to 5 seconds for door opening and closing is reasonable for normaloperations.(R5,R25)

ocbbaad ttPtPt ++= Equation 4-3where:td = average dwell time (s);Pa = alighting passengers per bus through the busiest door (p);ta = alighting passenger service time (s/p);Pb = boarding passengers per bus through the busiest door (p);tb = boarding passenger service time (s/p); andtoc = door opening and closing time (s).

Impact of Wheelchair Movements on Dwell Time

All new transit buses in the United States are equipped with wheelchair lifts orramps. When a lift is in use, the door is blocked from use by other passengers.

Typical wheelchair lift cycle times are 60 to 200 seconds, while the ramps used inlow-floor buses reduce the cycle times to 30 to 60 seconds (including the timerequired to secure the wheelchair inside the bus). The higher cycle times relate to asmall minority of inexperienced or severely disadvantaged users. When wheelchairusers regularly use a particular bus stop, the wheelchair lift time should beincorporated into the average dwell time. When wheelchair movements are rare,their impact on dwell time is accounted for by dwell time variability, discussed laterin this chapter.

Impact of Bicycles on Dwell Time

A growing number of transit systems provide folding bicycle racks on buses.When no bicycles are loaded, the racks typically fold upright against the front of thebus. (Some systems also use rear-mounted racks, and a very few allow bikes on

board on certain long-distance routes.) When bicycles are loaded, passengers deploythe bicycle rack and load their bicycles into one of the available loading positions(typically two are provided). The process takes approximately 20 to 30 seconds.When bicycle rack usage at a stop is frequent enough to warrant special treatment,average bus dwell time is determined using the greater of the passenger service timeor the bicycle loading/unloading time.



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Clearance Time

Once a bus closes its doors and prepares to depart a stop, there is an additionalperiod of time, known as the clearance time,when the loading area is not yet availablefor use by the next bus. Part of this time is fixed, consisting of the time for a bus tostart up and travel its own length, clearing the stop. When buses stop in the trafficlane (on-line), this is the only component of clearance time.

The time required for a bus to startup and travel its own length is fixed;re-entry delay is dependent on trafficvolumes in the curb lane.

When buses stop out of traffic (off-line), there is another component to clearancetime: the time required for a suitable gap in traffic to allow the bus to re-enter thestreet. This re-entry delaydepends on the traffic volume in the curb lane and increasesas traffic volumes increase. The delay also depends on the influence of upstreamtraffic signals, which may create long gaps in traffic, followed by periods of timewhen a constant stream of cars passes the stop. Some states have laws requiringmotorists to yield to busesre-entering a roadway; depending on how well motoristscomply with these laws, the re-entry delay can be reduced or even eliminated.

Many transit agencies avoid using off-line stops on busy streets in order to avoidthis re-entry delay. However, many roadway agencies prefer off-line stops to avoiddelays to other traffic and to reduce the potential for rear-end collisions betweenother vehicles and stopped buses. Exhibit 4-4 illustrates on-line and off-line stops,

and the problem of re-entry delay at off-line stops.Exhibit 4-4On-Line and Off-Line Loading

Areas

(a) On-Line (Portland, Oregon) (b) Off-Line (Albuquerque)

Estimating Clearance TimeVarious studies have examined the components of clearance time, with total

clearance times ranging from 9 to 20 seconds.(R40)The time required for a bus to startup and travel its own length to clear a stop is about 10 seconds. (R36,R38) At off-linestops, re-entry delay can be measured in the field or estimated from Exhibit 4-5.Notethat this exhibit applies only to random vehicle arrivals. If the flow of traffic past thebus stop is affected by a nearby upstream signal, or if buses must wait for a queuefrom a downstream signal to clear before they can re-enter the street, the HighwayCapacity Manualor simulation can be used to estimate the average interval betweenacceptable gaps (assumed to be 7 seconds in the absence of other information).

Some states have passed lawsrequiring vehicles to yield to busessignaling to re-enter the street, whichcan eliminate re-entry delay. Theselaws are discussed in Chapter 2.

Exhibit 4-5Average Bus Re-Entry Delay(Random Vehicle Arrivals)

Adjacent LaneMixed Traffic Volume (veh/h)

Average Re-EntryDelay (s)

100 1

200 2300 3400 4500 5600 6700 8800 10900 12

1,000 15

Exhibit 4-5 applies only to off-linestops where buses must yield toother traffic when re-entering astreet, and only when the stop islocated away from the influence of asignalized intersection.

SOURCE: Computed using HCM 2000 unsignalized intersection methodology (minor street right turn at a stopsign), assuming a critical gap of 7 seconds and random vehicle arrivals. Delay based on 12 busesstopping per hour.



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Dwell Time Variability

Not all buses stop for the same amount of time at a stop, depending onfluctuations in passenger demand between buses and between routes. The effect ofvariability in bus dwell times on bus capacity is reflected by the coefficient of variationof dwell times (cv), which is the standard deviation of dwell times divided by theaverage (mean) dwell time. When cvis zero, all dwell times are the same. When cvis

1.0, the standard deviation of dwell times is as large as the mean dwell time, meaningthat approximately one in three buses will have a dwell time twice as large as theaverage dwell time.

Coefficient of variation of dwelltimes.

Based on field observations of bus dwell times in several U.S. cities, (R36) cvtypically ranges from 0.4 to 0.8, with 0.6 recommended as an appropriate value in theabsence of field data. Dwell time variability is influenced by the same factors thataffect dwell time.

If a series of dwell time observations were to be plotted, they would form anormal distribution similar to the one shown to the left. A narrower distribution witha higher peak would indicate less variability, while a wider distribution with a lowerpeak would indicate greater variability.

Standard normal distribution.

P(t)

tZ0

Bus loading area capacity is maximized when a bus is available to move into a

loading area as soon as the previous bus vacates it. However, this condition isundesirable for several reasons: (1) bus travel speeds are reduced, due to the timespent waiting for a loading area to become available, (2) bus schedule reliabilitysuffers because of the additional delays, and (3) buses block traffic in the street forlonger periods of time. Consequently, bus capacity analysis incorporates the conceptof a failure rate that sets how often a bus should arrive at a stop only to find allloading areas occupied.

Failure rate.

The failure rate is used in combination with dwell time variability and theaverage dwell time to provide an operating marginthat is added to the dwell time andthe clearance time to make sure that failures do not happen more often than thedesired rate. In effect, the operating margin is the maximum amount of time that anindividual bus dwell time can exceed the average without creating the likelihood of abus stop failure when the number of buses scheduled to use the stop approaches itscapacity. The lower the desired failure rate, the greater the operating margin andschedule reliability, and the lower the loading area capacity. Conversely, the greaterthe allowed failure rate, the lower the operating margin and schedule reliability, andthe greater the loading area capacity.

Operating margin.

From statistics, the area under and to the right of a given point Zon a normaldistribution curve (such as the shaded area in the diagram above) represents theprobability that any given buss dwell time will be longer than that amount. Thedwell time value ticorresponding to Zis incorporated in Equation 4-4:

Standard normal variable Z.

s

tt

s

tZ diom

== Equation 4-4

where:

Z = standard normal variable corresponding to a desired failure rate;s = standard deviation of dwell times;tom = operating margin (s);Probability of bus stop failure.

0%

100%

0

Z0%

100%

0

P(busstop

failure)

t

P(t

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