Bus Priority Guidelines Nov 2003

November 2003

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IntroductionBus priority is the allocation of road space ortraffic signal time that gives buses anadvantage compared to usual operatingconditions. For example, a carefully located buslane allows buses to overtake queued traffic.Likewise a green signal extension can be usedto prolong the green time to enable a bus, onceit is detected, to clear an intersection.

Increasing general road capacity such as addingthrough, right or left turn lanes at intersections,or adding another lane to the road should not beconsidered as bus priority measures. Whilecapacity improvements do deliver benefits tomost road users, including buses, it is unlikelythese benefits will be maintained into thefuture. As congestion increases, the benefitsinitially provided to buses will be eroded.

In late 2004, it is expected that Austroads willpublish the Guide to Traffic EngineeringPractice, Part 16 – On-Road Public Transport.Until this is available, guidelines written byother jurisdictions can be used to obtainadditional information on bus priority principlesand design. One such document is Bus PriorityMeasures: Principles and Design being draftedby the Western Australian Department forPlanning and Infrastructure.

The Western Australian document provides anoverview of a number of methods of allocatingroad space and signal time to provide priorityfor buses. The information is short and concise,and conveys the general principles for a varietyof priority techniques. A copy of this draftdocument can be obtained from the Road BasedPublic Transport Section at VicRoads. Readersare encouraged to review these techniques toidentify measures appropriate to their situation.

The Road Based Public Transport Section atVicRoads is collating information on pastprojects into a database. Over time, this willprovide a history of bus priority projects, theircosts and their benefits.

A common problem for buses in built up areas isthat they are often delayed by queues of traffic,particularly during peak hours. Useful buspriority measures are required that can beretrofitted to existing roads and are acceptablein the trade-off between stakeholders. Thefollowing sections outline particular measuresthat are useful in these situations.

Bus Priority Guidelines

Bus Priority GuidelinesBus Priority GuidelinesBus Priority GuidelinesBus Priority GuidelinesBus Priority Guidelines

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Figure 1a: “Before Bus Lane” Cross-section Figure 1b: Parking prohibited during peak periods for apeak period bus lane

Bus lanesBus lanes separate buses from other traffic,enabling them to avoid traffic congestion. Buslanes can be provided in kerbside, median orcentre lanes. At some locations, a bus lane mayoperate in the opposite direction to traffic(contra-flow lane).

Kerbside bus lanes typically operate duringpeak-periods and allow parking during non-peak periods. On roads where there are noclearways (figure 1a), space for the bus lanecan be created by prohibiting parking duringthe peak period (figure 1b). However, on a roadwhere there are clearways, as shown in figure2a, it is more difficult to find space. The peak-period traffic lane could be removed andreplaced with a bus lane. To offset some of thereduction in road capacity, a transit lane couldbe provided instead of a bus lane. A transit lanecan be used by vehicles with more than oneoccupant as well as buses. The level of servicefor buses is less than a bus lane.

Alternatively, if adequate road width is availablegeneral traffic capacity could be maintained byproviding a five-lane cross-section with a tidal-flow central lane as shown in figure 2b.

At intersections, space may come fromconverting an existing through traffic lane to abus lane, changing a left turn lane into a buslane but allow left turning traffic to use it. Insome cases, widening of the road may be possible.

Information on the required signs and line-marking for bus and transit lanes is illustratedin VicRoads (2001) Traffic Engineering ManualVolume 2, Signs and Markings, and StandardsAustralia (2000) AS1742.12 Manual of UniformTraffic Control Devices, Part 12: Bus, Transit,Tram, and Truck Lanes.

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Figure 2a: “Before Bus Lane” Cross-section Figure 2b: Five lane cross-section to maintain generaltraffic capacity


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Set back bus lanesThe continuous bus lane previously describedcan impact on the capacity of the road if thenumber of lanes at the intersection for generaltraffic is reduced. One method of deliveringbus priority but maintaining existingintersection capacity is to set back the bus lanefrom the intersection, and allow general trafficand buses to use the approach lane.

The set back distance should be such thatbuses can always get to the end of the “greentime queue length” and hence travel throughthe intersection at the end of the green throughphase. Refer to figure 3. For example, if a laneof 15 cars can on average travel through anintersection during the green time, then a buslane could be provided to ensure that the busbecomes the fifteenth vehicle. This ensuresthat it gets through the intersection in onesignal phase.

To determine the maximum set back distance,it is necessary to consider the shortest greensignal time and calculate the number ofvehicles that can get through in this time. Thisis straightforward if it is a through lane. If it isa through and left lane, the number of leftturning vehicles, the volume of pedestrians,and their impact on delaying the through trafficwill need to be taken into account. Whilsttheoretical calculations for the set back positionare possible, on-site observations should also beundertaken.

If through traffic is using the left hand lane,adequate merging distance should be providedbefore a new bus lane commences downstreamof the intersection.

On a road where it is difficult to prohibit carparking along its entire length during peakhours, a partial approach may be possible.Figure 4 shows the use of a set back bus lane inconjunction with a short midblock bus lane.This allows buses to enter a bus lane, bypassthe rear of the stationary queue and havepriority up to the set back location.

Set back bus lanes are being widely used inLondon UK, as part of the work beingundertaken by Transport for London and theLondon Bus Initiative. A publication producedby the London Bus Initiative “Bus Lane andJunctions: How Close Can You Get?” (June2002) provides detailed guidance on set backbus lanes but in the London context. Many ofthe principles discussed in these guidelines aretransferable to Australia. A copy of thispublication is available from the VicRoads RoadBased Public Transport Section.

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Figure 3: Setback peak period bus lane with midblock buslane

Figure 4: Setback peak period bus lane with shortmidblock bus lane


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Short bus lanes at traffic signalsA short bus lane at traffic signals can be used inconjunction with allowing buses to travel in, andthen proceed straight ahead from a left turn sliplane. Buses receive an advantage as they canjoin the free flowing left-turn traffic, avoidqueues in the adjacent lanes, and stop at thebus stop at the stop line. Refer figure 5.

To avoid having to provide a bus lane on thedeparture side of the intersection, a “B” trafficsignal lantern can be used to provide an earlystart for buses or a separate bus phase at theend of the green time.

In addition to these treatments, it is importantto review the length of the left turn slip lane.The optimum length is one that is longer thanthe peak hour queue length, allowing buses tobypass the entire queue. If this is not feasible,the lane should then be longer than themaximum green time queue length as thisallows buses to queue jump one green phaselength of general traffic. It should be noted thatif the left turn lane is shorter than the greentime queue length, there are still some benefitsfor buses, particularly if there is a bus stop onthe slip lane traffic island. These three leftturn lane lengths are illustrated in figure 5.

Figure 5: Short bus lane at signals in conjunction with left-turn slip lanes

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Buses getting out of side streetsLocal bus services operating on residentialstreets need at some point on their route toturn right from a local street onto an arterialroad. If the intersection is unsignalised, therecan be significant delays during peak hours,waiting for a gap in the traffic on the arterialroad. This delay can be variable, and thereforeaffect the reliability of the bus travel times.This problem can also affect left-turning buses.

Fully signalising the intersection may addressthis problem. However this is a costly solution,adds another set of signals to the main road,and may lead to an increase in traffic using thelocal street. Additional traffic may also erodesome of the benefits of the signals.

Alternatively, buses can be detected at the stopline on the side road, and nearby pedestriancrossing signals on the main road activated. Thisprovides a window of time for the bus to exitthe side road. To advise main road users of thereason for a red signal, signs saying “Bus On SideRoad May Activate Signals” should be installed.

The use of selective bus detection is possible,equipping each bus with technology tocommunicate with the traffic signal controller.A low cost and reasonably effective alternativeis to use two pavement induction loops asshown in figure 6. These work on the principle

that a large vehicle such as a bus will coverboth loops at the same time, while a smallvehicle will not.

The optimum location for the pedestrian signalson the main road is to the left of the bus wantingto turn right from the side street as shown infigure 6. If the pedestrian signals are located tothe right of the bus, then the bus may havedifficulty getting into the traffic queuing at thesignals. If this is the only feasible option, thenmeasures need to be taken to ensure that thebus can turn right when these signals are red.The pedestrian signal location is less importantif the bus is turning left.

This concept has been proven where thepedestrian signals are up to 150 m from theside street. For distances over 100 m,consideration should be given to using a radiolink rather than cabling to the traffic signalcontroller.

The justification for installing pedestrian operatedsignals to assist buses needs to account forpedestrian demand at the site and the needs ofbuses. If the warrants for the provision ofpedestrian operated signals (refer VicRoads(1999), Traffic Engineering Manual Volume 1) arenot met, then a judgement needs to be made toassess the total benefits provided by the signals.

Figure 6: Utilising pedestrian operated signals to assist buses exiting side streets


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www.vicroads.vic.gov.auVicRoads Publication Number 01325

Traffic signal priority for busesThere are a number of traffic signal measuresthat can be used to provide priority for buses atintersections. However, to fully utilise many ofthese measures, a system for detectingapproaching buses needs to be in place.Detection and vehicle tracking systems arebeing introduced to metropolitan Melbourne,predominantly through the SmartBus program.Information on the SmartBus Program can beobtained from www.doi.vic.gov.au.

Rather than providing detailed guidance onsignal priority at this stage of the developmentof these guidelines, it is proposed to referreaders to the following two references.

Bus Priority Measures: Principles andDesign drafted by the Western AustralianDepartment for Planning and Infrastructureincludes general material on:

� Passive Signal Priority including reducedcycle times, priority movement repetitionin the cycle, green priority weighting,phasing design, signal linking for busprogression, and diurnal phasing variation,and

� Active Signal Priority including greenextension, green early start, special phase,phase suppression, priority phasesequences, phase compensation, flexiblewindow stretching, and priority green andB-lights.

Draft Signal Priority Guidelines have beenprepared by VicRoads’ Road Based PublicTransport Section, and can be made available onrequest. They outline a range of passive andactive signal priority measures for buses andtrams. Many of these measures can be used inconjunction with some form of bus lane.

Further reading on bus prioritymeasuresAustroads (2002) A Guide for TrafficEngineers – Road-Based Public Transport andHigh Occupancy Vehicles.

Department of Infrastructure (2001) TramImprovement Tool Box.

Department of Planning and Infrastructure- Western Australia (2003) Draft Bus PriorityMeasures: Principles and Design.

London Bus Initiative (2000) Bus Lanes andJunctions - How Close Can You Get?

Standards Australia (2000) AS1742.12 Manualof Uniform Traffic Control Devices, Part 12: Bus,Transit, Tram, and Truck Lanes.

VicRoads (2001) Traffic Engineering ManualVolume 2, Signs and Markings.

For further information on road basedpublic transport design standards, pleasecontact:

ManagerRoad Based Public TransportVicRoads60 Denmark StreetKew Vic 3101Tel: (03) 9854 2441Fax: (03) 9854 2918

Bus Priority Guidelines Nov 2003

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