bertini.eng.usf.edubertini.eng.usf.edu/courses/558/kai_tspreport.pdf · 2003-04-08 · phase and...

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Project PrincipalWayne Kittelson

Project ManagerJohn Ringert

Key StaffPeter KoonceKaren GieseScott Beaird

City of Portland Project ManagerWillie Rotich

Key City StaffBill KloosGabriel JavierPaul Zebell

Kittelson & Associates, Inc.

610 SW Alder Street, Suite 700Portland, OR 97295

January 2003

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S E C T I O N 1Executive Summary

Section 1: Executive Summary | 5

Executive Summary

his report provides a summary of the TransitSignal Priority system implemented in the City

of Portland. The implementation team includedthe City of Portland, TriMet, the Oregon Departmentof Transportation, and a Consultant Team led by Kit-telson & Associates, Inc. This report documents thedevelopment of the system, implementation, and les-sons learned by the Project Team.

OVERVIEW OF TRANSIT SIGNALPRIORITY FUNDAMENTALS

Transit signal priority (TSP) is an operational strategythat facilitates the movement of in-service vehiclesthrough signalized intersections. The objective oftransit signal priority is to modify the normal signaloperation to better accommodate transit vehicles,which can result in increased transit operating speedsand reduced travel time variability by reducing thesignal delay at signalized intersections.

Transit signal priority can be implemented in a vari-ety of ways. In Portland, the Project Team used a vari-ety of passive and active treatments to create a moreefficient system. Passive strategies attempt to accom-modate transit operations through the use of pre-timed modifications to the signal system that occurwhether or not a bus is present. These adjustmentsare completed to benefit transit while minimizing the

impact to other vehicles. The pas-sive strategies utilized transit opera-tions information, such as bus traveltimes along street segments, tomodify signal timing coordinationplans.

The City of Portland has a long his-tory of implementing active strate-gies to improve transit performance,including queue jump lanes andspecial signal phases. Active strate-gies such as signal priority seek tochange the signal timing based on apriority request from a transit vehi-cle. The ultimate goal of a signalpriority system is to use requestsfrom the buses to adjust traffic sig-nal operations so the transit vehiclesarrive at appointed locations at thecorrect times.

The objective of transit signal pri-

ority is to modify the normal signal

operation to better accommodate

transit vehicles, which can result in

increased transit operating speeds

and reduced travel time variability.

T

Portland is renowned for its innovative use of passive and active strategiesto improve transit performance.

SYSTEM COMPONENTS

Portland’s signal priority system consists of three basiccomponents: an automatic vehicle location system,bus detection, and traffic signal priority. The automat-ic vehicle location system is used to make informeddecisions regarding the priority request. Once the pri-ority request is placed, the bus must then be detectedby the traffic signal and the traffic signal must acceptthe request and activate priority.

6 | Section 1: Executive Summary

Automatic Vehicle Location SystemTriMet has been using Automatic Vehicle Location(AVL) to monitor and control its bus operations since1998. The AVL system uses on-board GPS receivers tomonitor the buses via the Bus Dispatch System (BDS), which was developed by Orbital Sciences Corpora-tion. The BDS system is connected to the bus’ on-board computer that contain route and scheduleinformation, allowing the bus to determine schedulestatus on a real-time basis. This “Smart Bus” systemonly activates the emitter when the bus is on route, in-

service for passengers, has its doorsclosed, and is running late. The thresh-old for determining whether the bus islate is set at 90 seconds. Once the bushas reached this threshold and is con-sidered behind schedule, the emitterwill be active until the bus has regainedits on-time status, defined as being nomore than 30 seconds behind schedule.1

Exhibit 1 highlights the decision frame-work for emitter activation.

Bus Detection SystemA particularly challenging decision forsuccessfully implementing transit signalpriority is deciding when to place a call.A call placed too late during the busphase can result in a missed opportuni-ty. A call placed too soon can result inthe provision of green time that cannotbe used effectively.

The Opticom system uses data that canbe transmitted from the bus to the traf-fic signal via an emitter and an opticaldetector. An emitter mounted on thebus is activated to send an encodedmessage to the traffic signal. A detectorlocated at the intersection receives thesignal and converts it to a message tothe controller. A phase selector within

EXHIBIT 1Decision Framework for Emitter Activation

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1At this point, the emitter stops requesting pri-ority until the bus is behind schedule again.

the controller cabinet makes the request for prioritywithin the traffic signal controller and also logs theinformation within the unit.

Traffic Signal TimingThe City of Portland uses the Wapiti MicrosystemsSoftware for its traffic signal software. This softwareprovides priority and preemption options as well as arange of recovery options to reduce bus delays. Thesignal priority strategies are in place throughout theday while buses operate on the system. Priority can berequested on any approach to the intersection.

EXHIBIT 2General Signal Priority Concept

Bus approaches red signal

RED TRUNCATION GREEN EXTENSION

Bus approaches green signal

Signal controller detects bus;terminates side street green phase early

Signal controller detects bus;extends current green phase

Bus proceeds on green signal Bus proceeds on extended green signal

SIGNAL CONTROLLER SIGNAL CONTROLLER

Section 1: Executive Summary | 7

During this implementation, red truncation andgreen extension are utilized to provide priority.Exhibit 2 illustrates both red truncation and greenextension associated with an active signal priorityimplementation.

The maximum extension is constrained by intersec-tion elements, but range from zero to forty seconds.The truncation also is dependent upon the configura-tion of the intersection. Exhibit 3 summarizes some ofthe limitations associated with the signal timing as itrelates to bus operations.

RESULTS

Analysis shows that a 2- to 3-minute reduction in trav-el time has been obtained from the transit signal pri-ority application on Barbur Boulevard, which is a 8 to

8 | Section 1: Executive Summary

11% reduction in the travel time during the eveningpeak hour. During periods of lower overall traveltime, the improvement to travel time is less signifi-cant. A significant reduction in travel time variability,19% in the morning peak hour, yields important sav-ings in operating costs.

CONCLUSIONS

This project shows that signal priority can improveschedule reliability and reduce signal delay for busesat intersections. The following report describes theexperiences of the City of Portland, TriMet, ODOT,and the Consultant Team through the development,implementation, and evaluation stages of this exten-sive Transit Signal Priority System.

Parameter Limitation Comment

Pedestrian Detection

Lack of pedestrian detection (push buttons foractuation) requires the opposing pedestrianphase to time every cycle

Presence of pedestrian detection increases thepotential responsiveness of the intersection toserve transit

Pedestrian TimingTime for Flashing Don’t Walk can not bereduced in any case

Pedestrian detection reduces the need torecall pedestrian phases each cycle, therebyimproving the responsiveness to transit

Multi-phase intersections

Phase skipping is not allowed in the State ofOregon, thus minimum vehicle times andclearance times must be considered for allphases (Legislative limitation)

Additional phases at intersections increase theamount of required time for service

Cycle lengths

Low cycle lengths reduce the flexibility of theengineer to extend the timing provided to thebus, although may provide better responsive-ness overall

The trade-off between flexibility and efficiencyat the intersections has been consistently dis-cussed, lower cycle length typically improvesbus operations

EXHIBIT 3Traffic Signal Timing Considerations for Signal Priority

One challenge of transit signal priority is how to improvetransit without negatively impacting pedestrians.

IntroductionS E C T I O N 2

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TEA-21 Signal PriorityTechnical Report

Section 2: Introduction | 11

Introduction

PROJECT BACKGROUND

Public transit is an important component of the trans-portation system in the Portland metropolitan area. Amajority of the local transit service is provided bybuses, and overall travel time isa primary means by which tran-sit riders judge the quality ofservice they receive. Therefore,transit will become a moreattractive travel option if themagnitude and variability of itstravel time requirements can bereduced. For this reason, theCity of Portland, TriMet, andthe Oregon Department ofTransportation (ODOT) haveteamed together to improvethe movement of public transitand emergency response vehicles by installing anOpticom-based signal priority system which can beused to provide both priority to transit vehicles thatare behind schedule and full pre-emption for certainemergency vehicles.

The current project is the result of several years ofexperimentation with various techniques (Kloos andTurner). The current system that has been imple-mented uses a 170 HC11 traffic controller, which is anevolutionary piece of hardware, as part of an eventualupgrade to a 2070-like Advanced Traffic Controller(ATC). The Wapiti software used by the City, the Ore-gon Department of Transportation (ODOT), andmost of the neighboring jurisdictions has beenupgraded to provide added bus priority features. Theimplementation allows green extension for the busphase and red truncation when in a non-bus phase(s)while also maintaining coordination. The detectionsystem used for the project was the 3M Opticom sys-tem and an automatic vehicle location (AVL) system isused to control the emitter.

TRANSIT SYSTEM DESCRIPTION

TriMet is the regional transit agency that serves thethree-county area of Portland, Oregon, encompassingthe counties of Multnomah, Washington, and Clacka-mas. TriMet has continued to increase their transitridership by offering exceptional service and continu-ally evaluating and improving their system.

TriMet has developed an ITSplan to ensure the Portlandregion is well prepared to real-ize the benefits of ITS. TriMethas planned projects that sup-port regional integration, buildon the agency’s existing infra-structure, and offer opportuni-ties for future ITS expansion(Parsons Brinkerhoff, Batelle).One of the twelve projects thatare the included in this plan is

signal priority. Initially the signal priority project willprovide priority at 250 traffic signals on seven busroutes within the City of Portland. The total projectcost was $4.5 million with initial field installation ini-tially estimated to be complete in July 2001 and field-testing estimated to be complete by Summer 2002.

The City of Portland, TriMet, and

the Oregon Department of Trans-

portation (ODOT) have teamed

together to improve the movement of

public transit and emergency

response vehicles.

Encapsulated in TriMet’s recent improvements is anew outer design on the buses.

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12 | Section 2: Introduction

TriMet has been using Automatic Vehicle Location(AVL) to monitor and control its bus operation for twoyears. The AVL system uses on-board GPS receivers tomonitor the buses via the Bus Dispatch System (BDS).The BDS system, developed by Orbital Sciences Cor-poration, is connected to the on-board computer oneach bus. This computer contains the route andschedule information for that bus. Integration of thisinformation allows the bus to determine schedule sta-tus on a real-time basis. This permits the applicationof the Smart Bus concept, which will only allow thebus to activate the Opticom emitter when the bus isbehind schedule and meets other specified criteria.

TRANSIT SIGNAL PRIORITYOVERVIEW

Transit signal priority treatments include passive,active, and real-time priority as well as preemption.Passive strategies attempt to accommodate transitoperations through the use of pre-timed modifica-tions to the signal system. These adjustments are com-pleted manually to determine the best transit benefitwhile minimizing the impact to other vehicles. Passivepriority can be simple changes to the signal timing, orsystemwide retiming to address bus operations. The

strategies can utilize transitoperations information such asbus link travel times to deter-mine signal timing coordinationplans.

Active strategies adjust the sig-nal timing after sensing thearrival of a bus. Depending onthe application and capabilitiesof the equipment, active prioritymay be either conditional orunconditional. Unconditionalstrategies provide priorityregardless of the transit vehiclestatus, i.e. regardless of the pas-senger loads or lateness, whereasconditional strategies providepriority only when a defined setof criteria are met.

Real-time strategies modify the priority requestsbased on the specific circumstances at the signalizedintersections. Currently, the active strategy the Cityhas employed is a first-in, first-out operation. A real-time strategy would use more information regardingbus status and the presence of other buses to deter-mine the class of priority necessary.

Preemption could be classified separately because itresults in changes to the normal signal phasing andsequencing of the traffic signal. Preemption is mostcommonly associated with emergency response vehi-cles and trains. These vehicles typically require thebenefit of proceeding through an intersection unin-terrupted and can pose a great danger to other vehi-cles if the vehicles are not stopped prior to the arrivalof the emergency response vehicle or train. Preemp-tion affects the normal operation of the traffic signaland the resulting traffic flow, which has the potentialto impact the safety and efficiency of the intersection.One of the most important effects is the disruption ofcoordination between traffic signals, which may resultin significant congestion.

As TriMet’s ridership continues to grow, the City of Portland is looking forways to continue to expand and enhance service.

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Section 2: Introduction | 13

The City of Portland, like many other agencies imple-menting bus priority, is focused on providing activepriority that adjusts the signal timing to accommodatebuses while remaining in a coordinated system of traf-fic signals. Portland's system is conditional becausethe AVL system uses a set of criteria to provide prior-ity only when needed.

SIGNAL PRIORITY IN PORTLAND

Portland has a long history of providing signal priori-ty for transit. The light rail system, MAX, began serv-ice in 1986 with high priority or preemption at manyof the signals in Portland. The level of priority hassteadily increased, allowing more efficient travelbetween the MAX stations.

Bus priority experience in Portland has includedthree field tests conducted by the City of PortlandBureau of Transportation: the Powell Boulevard PilotProject in 1993, the Multnomah Boulevard test in1994, and the Tualatin Valley Highway test in 1996.The Powell Boulevard test has been the most publi-cized of the three (Kloos, Danaher, Hunter-Zaworski).

This study evaluated several detection technologiesfor inclusion in the system. The technologies includedMcCain’s TOTE, Detector Systems’ LoopComm, and3M’s Opticom system. The signal priority algorithmswere limited in these tests to preserve traffic signalcoordination. In each of these tests, the City of Port-land worked with the transit agency, TriMet to deter-mine the effectiveness of the program.

The selection of Opticom units for the project came asa result of the Powell Boulevard Study and discussionswith key stakeholders throughout the Portland-metro-politan area. The Opticom system by 3M was chosenfor the following reasons:

■ Opticom units are standard in the suburbs foremergency vehicle preemption and this choicemakes expansion easy

■ The City of Portland Fire Bureau desires to reach100% coverage within the City to improve emer-gency vehicle response times

■ The optical detectors allow flexible range setting

■ The City did not want another piece of hardwarethat would increase maintenance costs.

PROJECT SCOPE

In the TEA-21 Signal Priority Project,the City of Portland and TriMet pro-vided active conditional priority atapproximately 250 traffic signalsusing 3M’s Opticom System. New sig-nal controller software was developedto be compatible with the OpticomSystem and provide capabilities need-ed to meet the City of Portland andTriMet requirements for successfulsignal priority. The implementationalso included the development of thebus priority signal timing plans andfield implementation of the con-trollers, software, timing plans, andthe Opticom System at each of theintersections. In addition, the projectincluded collection and evaluation of

Portland’s signal priority system helps to better integrate the bus sys-tem with MAX, and provides preemption for emergency vehicle toimprove response time.

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14 | Section 2: Introduction

Automated Vehicle Location (AVL) data to determinethe level of improvement of bus operations with theimplementation of signal priority.

PROJECT TEAM

This project was led by the City of Portland BureauOffice of Transportation but was a collaborative effortwith TriMet, the Oregon Department of Transporta-tion (ODOT), and Kittelson & Associates, Inc. as theprime contractor. The City of Portland led day-to-dayefforts of contracting, review, and implementation.TriMet provided critical feedback on observationsfrom the field, areas for improvement, and evaluationof AVL data. The ODOT oversaw the project and pro-vided insight on specific issues. Kittelson & Associates,Inc. served as the prime consultant, coordinated the

work of the subconsultants (NWS Traffic Engineeringand Siemens Gardner Transportation Systems),designed the intersections for Opticom, developedthe signal timing plans, and worked with the agenciesto review and evaluate AVL data collected.

SCOPE OF THE REPORT

The remaining sections of this report document theactivities of the project. Section 2 provides an intro-duction to the project and a project background. Sec-tion 3 summarizes details regarding the intersectioncharacteristics that affect signal priority. Section 4describes criteria for establishing priority detectionrange settings. Finally, Section 5 highlights the use ofAVL data in the evaluation of the system.

Members of the project team work together to develop signal priority strategies thatcould be implemented in the field on the Division Street corridor (Line 4).

S E C T I O N 3Evaluation of

Intersection Criteria

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Section 3: Evaluation of Intersection Characteristics | 17


Evaluation of IntersectionCharacteristics

Every signalized intersection has distinct characteris-tics: lane widths, pedestrian crossing distances, trafficconditions, etc. These uniquecharacteristics determine theextent transit signal priority(TSP) can be implemented.These characteristics can gen-erally be classified into four dif-ferent areas: signal timing, busroute, traffic, or physical con-straints. The elements high-lighted in this section of thereport are specific to the experience with the Wapiticontroller software and 3M Opticom equipment.

SIGNAL TIMING CHARACTERISTICS

It is critical to understand the signal timing character-istics of an intersection before implementation of TSP.The existing intersection signal timing and operationdictates the amount of pri-ority that should be givento each approach. Theamount of transit prioritydepends on operatingmode (coordinated opera-tions versus free opera-tions), pedestrian timing,cycle length (if coordinat-ed), signal phasing, splits,time of day coordinationplans, and other elementsof signal timing. Several ofthese factors are discussedin the following sections;however, factors not listedbelow should still be con-sidered and a full under-standing of existing opera-tions is necessary to appro-priately implement TSP.

Coordinated vs. Free OperationsSignals may be either part of a coordinated system orindependent in free operation (no coordination). Anintersection may operate in either mode, dependingon the time of day and site conditions. The method ofsignal operation dictates the implementation of TSP

for a signal; coordination sug-gests constraints that are notpresent in the uncoordinatedor free mode. In free mode,priority is granted by reducingthe maximum green time forthe non-bus phases andincreasing the maximum greentime for the bus phase. Inmany cases, the maximum

times for each non-bus phase are shortened by 50%and the maximum time for the bus phase is increasedto provide green extension.

When a signal is operating in coordinated mode, it isconstrained by the local cycle and its zero point, whichdefines the relationship between adjacent intersec-tions. At this point during the cycle, the coordinated

The current implementation of TSP

in Portland relies on green exten-

sion or red truncation to provide an

advantage to the bus.

The project team assessed the unique characteristics of each intersection in thesystem to discern the appropriate level of priority a bus should be given. Thisintersection at SE 12th and Hawthorne Blvd. was especially challenging.

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18 | Section 3: Evaluation of Intersection Characteristics


phase must be in operation and thus phases can onlybe adjusted around this constraint. Essentially, thephases are adjusted to provide transit priority whileremaining coordinated beyond the current cycle, suchthat the signal can always return back to its coordina-tion at this point. This adjustment is consequentlylimited by the coordination, although the limitationoften still exceeds the amount of TSP desired at anintersection.

The current implementation of TSP in Portland relieson green extension or red truncation to provide anadvantage to the bus. When the signal is operating ina coordinated system, either the green time for thebus phase is lengthened or the red time for the bus isshortened. This is accomplished by changing theforceoffs for each phase while maintaining the “zeropoint” to keep the signal in coordination with the sys-tem. Exhibit 4 shows the decision framework for pri-ority at coordinated operations.

Pedestrian Timing, Recall Traffic signals withoutpedestrian actuation (seepicture) or push buttonsmust rely on a recall in thetraffic controller thatensures a pedestrianWALK indication will bedisplayed during eachcycle. Pedestrian recallcalls up the time necessary to pedestrian timing forspecific phases that do not have pedestrian actuation.For example, when pedestrian recall is on the non-busphase, the minimum pedestrian cycle timing (Walkand Flash Don’t Walk) will occur, potentially delayingthe bus.

The lack of pedestrian push buttons (thus necessitat-ing the use of Pedestrian Recall) at a signalized inter-section limits the amount of time available to shortena phase (provide red truncation to the bus phase). For

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EXHIBIT 4Decision Framework for Priority at Coordinated Operations

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example, when Phases 4 and 8 have pedestrian recallactivated, priority timing for Phases 2 and 6 is limit-ed; because Phase 4 and 8need to serve the Walk andFlash Don’t Walk each cycle,regardless of whether a pedes-trian is present at the intersec-tion. In the City of Portland,many intersection signals arebased on the pedestrian tim-ing requirements and can notbe modified to provide signifi-cant benefits for the red trun-cation plans.

In instances with pedestrianpush buttons, (without pedes-trian recall) the pedestrian timing must be taken intoaccount when providing priority. A signal prioritystrategy must be developed such that, in the event ofa pedestrian call, the signal is able to serve the pedes-trian timing without driving another phase to its min-imum or negatively impacting the bus phase. This isdone by providing priority for the “worst-case” sce-nario, assuming pedestrian timing will be called evenwhen Pedestrian Recall is not active.

In the City of Portland, bus priority signal timingplans were developed to allow each phase to fulfill itsminimum time inclusive of the pedestrian require-ments at the intersection. The development processconsidered the pedestrian activity and determinedwhat would be necessary to reduce the number oftimes during the day that vehicular traffic will experi-ence a phase driven to its minimum time by a pedes-trian. While this approach sometimes limited theamount of priority given to the bus, it ensured that,without the presence of Pedestrian Recall, if a pedes-trian phase were called, subsequent phases would notbe significantly impeded.

Cycle Lengths The cycle length at an intersection is the timerequired to serve each phase (movement) in a coordi-nated plan.

The cycle length impacts the extent to which signalpriority is provided in two different ways. The higher

the cycle length, the greater theflexibility to provide transit pri-ority. On the other hand, shortcycle lengths allow efficientoperations for buses (and otherusers) whose arrival may not beconsistent, such as a car travel-ing without stopping from oneintersection to another along anarterial. Planning of futuretransit signal priority projectsshould consider the opportuni-ties associated with buses onnon-coordinated phases, whichhave the greatest opportunity

for improvement, and cycle lengths, which providesubstantial flexibility in the priority implementation.

Phasing (Two-Phase versus Multi-Phase Signals) Two-phase signal timing plans are the simplest formof phasing for traffic control, and, simply stated, sep-arate the main street traffic from that on the crossstreet. Adding left-turn movements (typically identi-fied by left-turn arrows at an intersection) result inmulti-phase signal timing plans that can include up toeight phases.

Since the bus phase is provided priority by reducingor delaying the green time of other phases, havingonly two phases may limit the amount of time that canbe taken from the non-bus phase and given to the busphase. This is especially noticeable when the cyclelength is short and both of the phases have pedestri-an recall.

Multi-phase intersections present difficulties in pro-viding priority and specifically in determining howmuch to reduce non-bus green times; however, thereis typically more flexibility in having additional phas-es to steal time from.

In the City of Portland, priority was provided at two-phase intersections when possible. The priority was

The higher the cycle length, the

greater the flexibility to provide

transit priority. On the other hand,

short cycle lengths allow efficient

operations for buses (and other

users) whose arrival may not be

consistent.

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often constrained by the elements discussed above,however, providing even minimal priority benefitstransit travel time. At many intersections in the City ofPortland, the bus travels along the coordinated phase,which in a coordinated systemreceives the unused time asso-ciated with the non-coordinat-ed phases. The coordinatedphases typically receive a highpercentage of green timealready dedicated to the busphases. Thus, the added bene-fit of time might be a smallpercentage of the time beyondwhat is already provided in thesignal cycle.

Conversely, a bus on the non-coordinated phase willtypically not receive a high percentage of green time.Due to the amount of time already given to the coor-dinated phase, there may be more flexibility to pro-vide priority to buses on the non-coordinatedapproaches through green extension.

As with cycle lengths, planning of future transit signalpriority projects should consider the opportunitiesassociated with buses on non-coordinated phases,which have the greatest potential for improvement oftransit operation.

SplitsThe allocation of green time at an intersection is typ-ically representative of traffic patterns. Minimumtimes for each phase must be met and the excess (flex-ible) time in the cycle allocated to the bus phase,based on traffic characteristics. When adjusting splitsto provide priority, consideration must be taken sothat the adjustment does not dramatically impact thevehicular traffic on the non-bus phases. Thisapproach was aggressive but considerate of overallperson delay. If the splits are adjusted too much, thenon-bus approaches may experience noticeably high-er delays, resulting in longer queues.

Example:In most cases, priority was provided by adjusting thenon-bus phases by approximately fifty percent of thegreen time allocated to that phase in excess of the

minimum timing. For example,if a left-turn phase has a greentime of nine seconds and a min-imum green time of three sec-onds, then the adjustmentwould be three to four seconds.On movements with longergreen time allocations, theadjustment may be less thanfifty percent above the mini-mum timings. The amount of

priority also considered the number of buses at theintersection; where bus headways were long, the pri-ority was more aggressive. This approach resulted in areduction of green time that would not significantlyimpact traffic on non-bus approaches.

TRAFFIC AND OTHER CHARACTERISTICS

Traffic has a direct impact on the ability to providereliable and efficient transit service. Traffic patternsand the level of traffic congestion both contribute tothe amount of delay experienced by transit along aroute, especially at signalized intersections. Under-standing these elements at the intersection level isfundamental in providing appropriate transit signalpriority that does not needlessly elevate congestionand delay already experienced by drivers.

Time of Day/Directional Split During commuter hours, traffic patterns and conse-quently signal timing may vary depending on thepeak direction of traffic. For example, during themorning peak hour, the inbound (to downtown Port-land) direction typically is the peak direction.

By providing priority in both directions throughoutthe day, a bus traveling in the critical (e.g., peak)direction may not receive priority, because it has beenprovided to a bus traveling in a non-peak direction on

Traffic patterns and the level of

traffic congestion both contribute to

the amount of delay experienced by

transit along a route, especially at

signalized intersections.

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the previous cycle. This is of special concern consider-ing that a bus traveling in the peak direction is alsomore likely to need priority, due to congestion-caus-ing lateness. Likewise, a bus traveling in the non-peakdirection will not have as many passengers and thus itis not as critical to provide priority to that bus.

Buses traveling in the peak direction were providedmore aggressive priority if deemed necessary basedon knowledge of the route, the intersection, and traf-fic patterns in the area. This priority was sometimesprovided at the expense of non-peak direction move-ments.

Congestion and Queuing Congestion at an intersection may cause buses unnec-essary delay and, if significant enough, may causequeues to build up, preventing the bus from serving anear-side stop or from passing through the intersec-tion within one signal timing cycle.

When the bus approaches a heavily congested inter-section, aggressive priority should be provided if pos-sible. This is beneficial as the added green time orreduced red time for the bus phase will help dissipatecongestion and queues on the bus approach, helpingthe bus proceed through the intersection.

BUS ROUTE CHAR-ACTERISTICS

The bus routes for the Port-land TSP system were strategi-cally chosen based on a num-ber of factors. There are char-acteristics associated with eachof these routes as well as otherroutes in the vicinity thatimpact the priority providedfor transit at each intersection.Transit headways and crossinglines will not typically elimi-nate the ability to provide pri-ority; but when these elementsare considered at specific loca-

tions, the result will typically be a slightly less aggres-sive TSP approach that provides the most sensible sys-tem level solution. Essentially, as the time betweenbuses requesting priority is reduced, the more likely itis that the priority plan may become the default plan,thus resulting in significant changes to the signal tim-ing over the course of the hour.

Transit HeadwaysTransit headways, as addressed in signal priority, aredefined as the amount of time between buses servingdifferent routes arriving at the same location or stop.

Bus headway may impact the decision to provide pri-ority, since short headways may result in bus arrivalsthat occur every other cycle. In this case, the bus thatarrives on the second cycle may be affected negative-ly, because the software used by the City of Portlanddoes not allow back-to-back priority calls. In otherwords, if a bus proceeds through the intersection on apriority call, the signal controller must complete onefull cycle under normal operating conditions beforeanother priority call can be served. Thus, a busapproaching an intersection immediately behindanother bus (or from the opposite direction) will like-ly enter the detection range during the “second cycle”and not be given signal priority. Providing this second

Aggressive priority is provided in heavily congested areas to keep buses mov-ing through intersections.

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cycle helps ensure that the signalwill not fall out of coordination withthe system but has the potential toimpact the ability to grant priorityto the following bus. The currentsystem also lacks the ability to con-sider the lateness of future buses orto use criteria such as peak direc-tion to distinguish importance.

During the first phase of the City ofPortland’s TSP system implementa-tion, headways made it unlikely thatbuses would be affected by prioritycalls made during back-to-backcycles. In the cases where two busesdid serve a single intersection, pri-ority prevented the second busarriving at the intersection fromany significant negative impact dueto entering during the recoverycycle. Essentially, care was taken to adjust the timingswithout adjusting the start of green for a potential sec-ond bus. This allowed the recovery cycle to occur andthe bus to experience normal operations at the inter-section, limiting any additional delay due to movingthe start of green time for that approach.

For example, the traffic signals along the downtowntransit mall serve multiple routes resulting in shortheadways in the corridor. In this case, TSP would ben-efit only a limited number of buses while other buseswould be impeded by the priority given every othercycle. For this and other reasons, TSP was not imple-mented in this area.

Crossing LinesThe City’s grid network of streets and extensive tran-sit services results in transit lines crossing at numerousintersections. Line 9-Powell for instance, generallyruns east-west along SE Powell Boulevard. Line 14Hawthorne crosses SE Powell Boulevard at the SEPowell/SE 50th/Foster Road intersection. Similarly,Line 72 Killingsworth/82nd Avenue crosses SE Powellwhile on SE 82nd Avenue. At these intersections, pri-

ority was implemented on all four approaches to serveboth bus lines.

A potential conflict occurs when buses approach fromconflicting directions on the same cycle. The currentsystem uses a first-in, first-served approach, whichgives priority without consideration of ridership,degree of lateness, or other advanced criteria. Toaccount for this, the signal priority timing plan devel-oped for each approach identified the potentialeffects on other buses. If the bus priority is aggressivefor the east-west approach, then the north-southapproach buses may be impeded, since the priorityfor any given approach is provided by reducing thegreen time for the other approaches. Consideration ofpeak directions may also be warranted as discussedabove. For example, inbound bus trips during themorning peak hour may be provided more aggressiveTSP through the priority timing plans than the out-bound direction and vice versa during the eveningpeak hour.

It is important to note, however, in the case of the SEPowell Boulevard/SE Foster Road intersection, as well

Portland’s extensive transit system created unique challenges in imple-menting priority where two lines cross.

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as other intersections withcrossing lines, the bus priorityprovided was not as aggressiveon any of the approaches as itcould have been if no otherapproaches needed priority.This was also due in part topotential impacts to vehiculartraffic at this critical intersec-tion. While each approach willnot benefit from the mostaggressive timing plan that mayhave been provided, on a sys-tem level this is the most effec-tive solution when consideringbuses on conflicting approaches.

PHYSICAL CONSTRAINTS

The physical elements of an intersection such as busstop location, sight distance, and proximity toupstream signals may limit the amount of priority bylimiting the distance at which the detection range canbe set. Establishing the priority distance is a criticalportion of the implementation. Ideally, the detectionwould occur at the furthest upstream point to giveadvanced notice for the approach of the buses.Because the Opticom system results in an immediaterequest for service, the distance from the traffic signalfrom which the call is received dictates the length ofthe extension possible. In order to address the limita-tions, the detection range is set to provide a call thatwould take advantage the amount of priority timeavailable within the extension portion of the priorityservice. Essentially, the length of advance time thatcan be accommodated is limited by lack of knowledgeabout the desired time of service and limitations inthe controller software’s decision-making logic. Themaximum advance time is the length by which the busphase can be extended.

The goal of the priority distance setting is to allow thebus to pass through the intersection during the cur-rent green time based on the allotted extension timefor that approach and the assumed travel speed of the

bus at that location. If this dis-tance is limited by stop loca-tion, then the amount of prior-ity necessary may be signifi-cantly less than the priorityavailable through adjustmentof the signal timing. Thus, thesignal timing must be reevalu-ated, providing priority basedon the distance setting.

Bus Stop LocationsThe location of the bus stop isan important element for theimplementation of signal pri-

ority. The primary distinguishing feature is whetherthe bus stop is located near-side or far-side of theintersection. When the bus stop is located downstreamof the signal (on the far-side of the intersection), thestop location has no impact on the ability to providebus priority.

When the bus stop is located immediately upstream ofthe intersection (at a near-side location), boardings

The location of the bus stop is an

important element for the imple-

mentation of signal priority ...

When the bus stop is located imme-

diately upstream of the intersection

(at a near-side location), boardings

may reduce the ability of the bus to

use the priority call.

Boardings at this near-side bus stop at SE MilwaukieAve. and SE Powell Blvd., which is upstream from thetraffic signal, will affect the ability to use priority calls.

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may reduce the ability of the bus to use the prioritycall. Depending on the stop service percentage (asso-ciated with the time-of-day plan in the controller), thepriority strategy may be limited to request priorityafter the stop. While this results in a request for serv-ice that occurs close to the signal, it reduces the num-ber of priority requests that would not be utilizedbecause of the boarding that occurs at the near-sidestop. To address this constraint, the Project Team hassuggested a modification to the computer on-boardthe bus. In this modification, the bus would monitorthe stop requested to determine whether a stoprequest has occurred for the stop adjacent to the sig-nal. This would be especially helpful during theevening peak hour on the outbound buses. An addi-tional, more complicated modification would allowthe buses to send messages to the local controllerthat, in turn, could process these messages with agiven set of criteria used to make decisions related tothe priority requests.

The approach with the existing system for this projectwas to set the priority distance depending on the busstop service percentage. If the bus stop service was lessthan 25 percent, the near-side stop was disregardedand the full distance setting was applied. If the busstop service was greater than50 percent, the distance set-ting assumed the bus wouldstop and was set between thebus stop and the stop bar ofthe signalized intersection.While this approach accom-modates most of the buseswithin the priority given, ifthe bus does not need to stopto load or unload passengers,the amount of time needed tocross the stop bar from thepoint of detection is less thanthe amount of time providedthrough priority. This resultsin what is considered “wastedpriority” and unnecessary dis-ruption of other traffic. Ifthese near-side buses were

moved to the far-side, then the worst-case scenariowould be the bus traveling through the intersectionwith normal delay due to traffic characteristics at theintersection. Each of the buses then would have simi-lar travel speeds and, thus, the distance can be set toaccommodate those buses without having to accountfor any stops between the detection point and the stopbar. This allows the buses to take advantage of the fullamount of priority provided through the signal tim-ing plan.

Through the implementation stages of the City ofPortland’s TSP, intersections have been identifiedwhere near-side stops have significantly impacted thesignal priority. City and TriMet staff have workedtogether to determine the feasibility of moving near-side stops to far-side locations. Some of the near-sidestops have been moved to far-side and this approachhas been included in transit corridor streamliningprojects and considered in future transit plans. In thecases where the near-side stop remained at the near-side location, the distances were set as discussedabove; and the signal timing plans provided kept thebeginning of green for the bus approach at the samepoint in the cycle as during normal operations.Therefore, if a bus loaded passengers and was unable

Closely spaced signals like these in the Lloyd District, present unique challenges.

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to proceed past the stop bar before the clearanceinterval of the bus phase, the bus would not be imped-ed on the next cycle and would proceed through theintersection at the beginning of its normal green time.

Sight DistanceThe sight distance referred toin this project is the furthestdistance at which the Opti-com receiver at the signal candetect the priority signal fromthe emitter. If sight distance isblocked or limited and noadvance detector is provided,the emitter will not receivethe priority call or the call willbe dropped after the call isinitially placed, due to a loss of the signal between theemitter and receiver. This impacts not only theamount of bus priority but also impacts the ability forthe high priority/emergency vehicle preemption tooperate effectively. When sight distance is an issue,there are two approaches that can be taken.

First, the range setting can be set downstream of thesight distance concerns. For example, if there is a hor-izontal curve leading to the signalized intersection,the range can be set so the bus priority call will not beplaced until the bus exits the curve and has a constantline of sight to the Opticom receiver. This is an appro-priate solution when the sight distance issue is at adistance that allows the range setting to be set at areasonable distance.

The second option is to provide advanced detectionthrough an auxiliary receiver placed upstream of thesignal. This receiver is placed primarily for emer-gency vehicle preemption to provide a line of commu-nication with the signal controller through the tworeceivers. Transit vehicles also benefit from this auxil-iary detector. This method was used in several loca-tions in the City of Portland where the sight distancelimitations would not have allowed priority to be usedto provide maximum benefit for the buses.

Closely spaced signalsIn a number of situations, signal spacing was closeenough that the bus could request priority at both sig-nals. The result would be a bus call being placed fora signal before a bus cleared an upstream signal. If the

bus is delayed at the upstreamsignal, the call for the secondsignal may unnecessarily disrupttraffic flow. This has the poten-tial to limit the range setting dis-tance, thereby impacting theamount of priority given to thebus approach.

Through the implementation ofthe City of Portland’s TSP sys-tem, in the instance of closely

spaced signals, the range setting distance was typical-ly set so the bus would pass through the upstreamintersection before calling for priority at the intersec-tion, but there were some instances where requestingpriority at a group was an advantage.

SUMMARY

Elements of signal timing, bus route, traffic, and phys-ical characteristics were highlighted in this section ofthe report. Possible concerns for these characteristicsand the Project Team’s approach to addressing theseissues were discussed. These characteristics were high-lighted because of the impact they had on the TSPsystem implementation; however, it should be notedthat there may be other factors that affect the abilityto provide TSP along a route at specific locations. Asolid understanding of the transit and vehicular traf-fic operations and the existing signal timing at eachintersection is key to successful TSP implementation,which should result in more efficient transit opera-tions that is essentially transparent to the other usersof the system.

A solid understanding of the transit

and vehicular traffic operations

and the existing signal timing at

each intersection is key to successful

TSP implementation.

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S E C T I O N 4Detection Range and

Bus Stop Location

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Section 4: Detection Range and Bus Stop Location | 29


Detection Range and Bus Stop Location

The location of the bus stop at a particular intersec-tion is a key to determining the detection range forsignal priority. Included in this section are details onthe following:

■ Preferred Bus Stop Location

■ When Not to Change a Bus Stop Location

■ Recommended Changes to Bus Stop Locations

■ Streamline Project Improvements

The potential benefit of transit signal priority is influ-enced by multiple variables, many of which must beevaluated on an intersection-by-intersection basis.One of these variables is the location of bus stops rel-ative to the intersection. Generally, when applicationof signal priority is being considered, it is preferableto locate bus stops far-side of a signal rather thannear-side. Although far-side stops do not allow a busstopped at a signal to use that time to service passen-gers, they do permit greater flexibility and effective-ness of signal timing plans that offer greenextension (commonly referred to as length-en plans) than near-side stops. A busrequesting a green extension at an intersec-tion with a far-side stop should travelthrough that intersection during the cur-rent green phasew because it can use theextended green and it does not have tostop prior to the signal to service passen-gers. The primary difficulty with near-sidestops and transit priority is the negativeimpact of a bus calling for a green exten-sion, the signal extending the green, andthen the bus stopping at the near-side stop.In this scenario, the bus will likely wait alonger time to get a green indication in thenext cycle and side street traffic at theintersection may experience longer delays.For this reason, near-side stops should beconsidered for re-location to a far-side

location. However, the characteristics of each stopshould be considered individually before beingmoved.

NEAR-SIDE STOP CHARACTERISTICS

The City of Portland’s Transit Preferential Streets Pro-gram Source Book provides guidelines related to tran-sit improvements and stop relocation to the far-side ofthe intersection. Although far-side is the preferredlocation for bus stops at signals with signal priority,there are several circumstances where a near-side stopis acceptable or necessary. Circumstances in whichnear-side stops will operate acceptably are describedbelow.

No Priority Timing Available The existing signal timing, physical constraints and/orbus operations may limit the amount of priority avail-able at a particular intersection. In cases such as these,there is no short-term benefit to moving a near-sidestop to a far-side location. There could potentially bea long-term benefit as conditions may change and an

Moving bus stops would result in eliminating on-street parking,such as at the intersection of NE Sandy Blvd. and NE 24th Ave.

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30 | Section 4: Detection Range and Bus Stop Location


opportunity for priority timing may become available.Therefore, moving near-side stops to far-side wouldbe a good planning policy. One example of thisinclude the SE 20th Avenue/SEDivision Street intersection onLine 4 where the controlleroperates in fixed time modedue to the five legged intersec-tion and the short cycle length(70 seconds). The 12thAvenue/Burnside-Sandy Blvd.intersection is another locationthat operates fixed timethroughout the day.

Low Stop Service PercentageTriMet maintains a database containing the bus stopservice percentage for each stop. This stop servicepercentage is useful in determining which stopsshould be moved far-side to benefit from signal prior-ity. Near-side stops with a very low stop percentage

offer smaller benefits from being relocated. In thesecases, the probability of a bus being late, placing a callduring the green phase, and receiving a request for

service is very low. Generally,any location with a stop per-centage of under fifty-percentshould be further evaluatedbefore a decision is made tomove a stop. It is important toremember to consider all timesof the day; a location with a lowstop percentage in the a.m. mayexperience a high demand dur-ing the p.m. time period.

Surrounding Land Use Many times a near-side stop is located adjacent to amajor trip generator. In these cases, moving the stopto the far-side may not be desirable because it impactspedestrian accessibility and may require riders tocross through the intersection to access a particular

building. Also, existing land uses (i.e. on-street parking, outdoor dining areas,etc.) may make moving a stop to the far-side of an intersection undesirable foradjacent businesses.

Bus Transfer Locations

Often bus stops are located such that rid-ers transferring from one line to anothercan do so at one location. The photo-graph to the right shows a near-side busstop for Line 72 Killingsworth locatedadjacent to a far-side stop for Line 4Division. In this instance, transfersbetween the lines are maintained on thesame corner and passenger amenitiescan be combined. For these reasons, stoprelocation is not desirable and should becarefully considered. If all stops areplaced far-side, riders transferringbetween lines are required to crossthrough the intersection.

The crossing of Line 72 Killingsworth and Line 4 Division is an impor-tant transfer location. Moving the near-side stop to the far-sidewould require transferring passengers to cross the street.

Generally, when application of

signal priority is being considered,

it is preferable to locate bus stops

far-side of a signal rather than

near-side.

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Section 4: Detection Range and Bus Stop Location | 31


Investment in Capital Improvements

TriMet has invested significant resourcesinto improving the safety, appearance, andconvenience of bus stop locations. Shelters,bus curb extensions, and improved passen-ger waiting platforms are a few of the capi-tal investments that have been made atmany locations. To abandon these improve-ments for a far-side stop may not be pru-dent. However, factors such as curb exten-sions can reduce pedestrian crossing dis-tances, thereby reducing the signal timingconstraints at the intersection. The resultmay be an increase in the effectiveness ofthe signal timing settings even with a near-side stop.

RECOMMENDED CHANGESTO BUS STOP LOCATIONS

In the process of developing bus priority timings, Kit-telson & Associates, Inc. has made recommendationsto move stops from near side to far side to take advan-tage of the potential benefits signal priority can pro-vide. A coordinated effort between traffic and transitstaff has made the project more effective. Beyond spe-cific recommendations, the Project Team has workedto educate TriMet staff in the consideration of busstop locations as an important element of the Stream-line Project.

It is impractical to move stops that have undergone recent capitalimprovements, such as is the case at the intersection of NEBroadway and NE 12th Ave.

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32 | Section 4: Detection Range and Bus Stop Location


Automated Vehicle Location Data Collection

S E C T I O N 5

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Section 5: Automated Vehicle Location Data Collection | 35


Automated Vehicle Location Data

Automated Vehicle Location data was collected as partof the project for analysis of bus performance withand without priority. Initially, the implementation andAVL Data Analysis was intended to focus on Line 4 -Fessenden/Division but because of scheduling chal-lenges associated with the implementation of thatroute, the analysis was completed for Line 12 - Bar-bur.

AVL SYSTEM

TriMet has been using Automatic Vehicle Location(AVL) to monitor and control its bus operations since1998. The AVL system uses on-board GPS receivers tomonitor the buses via the Bus Dispatch System (BDS).The BDS system, developed by Orbital Sciences Cor-poration, is connected to thebus’ on-board computer, whichcontains the route and sched-ule information. Integration ofthis information allows the busto determine schedule statuson a real-time basis. This per-mits the Smart Bus concept,which will only allow the bus toactivate the Opticom emitterwhen the bus is behind sched-ule and if certain other criteria are met. These othercriteria include the following:

■ location of the bus in the metropolitan area (cur-rently only signals with the City of Portland areactivated and the emitter does not operate outsideof the City boundary),

■ determination if the bus is in route and in service(buses that are returning to the bus garage are notgranted priority because they are not on route),

■ determination if the bus is ready to proceed alongthe route (this is determined by a toggle activatedby the door opening, once the door is open thepriority emitter is turned off.

The AVL system allows TriMet staff to actively managethe buses and provide passenger information at keystops throughout the Portland-metropolitan area.

ANALYSIS

TriMet has documented the performance of the buseswith and without priority for several of the routes thathave been implemented. Evaluation of the bus per-formance has focused on three primary factors:

■ travel time,

■ travel time variability, and

■ on-time performance.

A detailed evaluation of the Barbur Boulevard corri-dor was undertaken to describe the benefits of signalpriority. The before-and-after evaluation was complet-ed for eight weeks, four weeks collecting data for eachscenario. The only change made between the before

and after scenarios was that sig-nal priority settings were acti-vated within the signal con-trollers in the field. Data wascollected to summarize thenumber of buses that wereusing priority throughout thecorridor in the “with priority”case.

TriMet’s AVL system recordsthe time and date each bus passes a bus stop along theroute. Each route has been cut into segments to delin-eate the effects at each traffic signal. The segmentsvary from 800 to 2,500 feet and include up to threesignals. TriMet’s AVL system records many differentpieces of data about every single time any bus passesby a bus stop. The system records arrival time near asegment to initialize the start of the segment time andsegment end time to identify the total travel time foreach segment. The links were established to identifythe improvements associated with each signal and todetermine changes necessary within the signal timingor detection range settings that were in the field. Thisprovides an opportunity for fine tuning and continu-

The evaluation of signal priority

has shown that not only are buses

travelling their route faster, but

they are arriving at stops more con-

sistently.

ResultsThe first part of the evaluation presents the effective-ness of signal priority in terms of overall travel time-savings along the Barbur corridor. This measure ofeffectiveness was collected for all buses that operatedwithin the corridor throughout the four-week studyperiod. The a.m. peak and p.m. peak trips were sepa-rated for this analysis.

Exhibit 5 presents travel time and coefficient of vari-ability of travel time (as a percentage of travel time).As shown in Exhibit 6, the outbound portion of thetravel shows a significant improvement in travel timeand variability in the p.m. direction while theimprovements were much less in the inbound direc-tion.

The second and more important review of the signalpriority in this implementation is the evaluation oftravel time change associated with buses that were lateenough to be granted priority throughout their trip,i.e. more than 90 seconds late (at the beginning)throughout the corridor as shown in Exhibit 7. Fromthe AVL data, it was determined that priority wasrequested for the entire trip on less than 40 percent ofthe trips studied.

This analysis shows that a 2- to 3-minute reduction intravel time has been obtained from the transit signalpriority application on Barbur Boulevard, which is an8 to 11% reduction in the travel time during the p.m.

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36 | Section 5: Automated Vehicle Location Data Collection


ous monitoring of the segments. The AVL system pro-vides other useful data, such as passenger counts,amount of time the door was open at a particularstop, location of wheelchair lift operations, etc. Fromthis data, it is possible to determine exact runningtimes of the buses.

Run time data was analyzed for over 5,000 bus tripsthroughout the study. Data was collected and analyzedfor two peak periods in both directions along eachroute. The a.m. morning peak and p.m. evening peaktrip start times represent the most congested timesalong these travel corridors.

Previous studies completed as a part of the PowellBoulevard Pilot Project indicated that signal timingchanges of this magnitude had insignificant impactson the traffic operations and a significant reduction ofoverall person delay. The traffic impacts associatedwith the bus operations was further minimized in thisimplementation by the priority criteria that were usedto determine whether the bus emits a call to the detec-tor. As described previously, priority was only request-ed if the bus was:

■ on route,

■ ready to proceed (its doors are closed),

■ within the City of Portland, and

■ late (based on the definition agreed to).

EXHIBIT 5Line 12 Barbur Boulevard Travel Time Summary (All Trips)

Direction PeakWith TSP Without TSP Differences

Travel Time Variability Travel Time Variability Travel Time Variability

Outbound AM 19.7 minutes 10.6% 20.1 minutes 25.5% 0.4 minutes 14.9

Outbound PM 24.2 minutes 10.2% 27.4 minutes 26.3% 3.1 minutes 16.1

Inbound AM 22.7 minutes 8.6% 23.1 minutes 10.8% 0.5 minutes 2.2

Inbound PM 22.1 minutes 9.3% 23.2 minutes 16.6% 1.1 minutes 7.3

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Section 5: Automated Vehicle Location Data Collection | 37


EXHIBIT 6Line 12 Bus Travel Time Summary (Late Trips Only)

EXHIBIT 7Run Time Distribution - PM Peak Trips

Direction PeakWith TSP Without TSP Differences

Travel Time Variability Travel Time Variability Travel Time Variability

Outbound AM 20.2 minutes 10.2% 20.8 minutes 29.3% 0.6 minutes 19.2

Outbound PM 25.6 minutes 9.6% 28.8 minutes 26.4% 3.2 minutes 16.7

Inbound AM 22.8 minutes 7.3% 23.3 minutes 10.1% 0.4 minutes 2.8

Inbound PM 22.2 minutes 9.2% 24.3 minutes 18.6% 2.1 minutes 9.4

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peak hour. During periods of lower overall traveltime, the improvement to travel time is less signifi-cant. a significant improvement in both the outboundtrips cases is the reduction it travel time variability,which reaches 19% in the a.m. peak hour. The triptravel time distribution is clearly exhibited in Exhibit7. This reduced travel time variability results inimproved on-time performance and reliability.

SUMMARY

The AVL system has shown that signal priority offersthe promise to improve schedule reliability andreduce travel time through traffic signals. The use ofthe AVL system in conjunction with the signal priorityreduces the number of requests to the traffic signalthereby increasing the aggressiveness of the signaltiming settings deployed.

38 | Section 5: Automated Vehicle Location Data Collection

The Project Team has identified some additionalenhancements that we have identified for a future ver-sion of the AVL software. These additional enhance-ments could be added to make the system smarterand include:

■ determination if the bus is preparing to stop dueto an on-board passenger request (this would onlybe necessary at intersections with near sidestops),

■ detection range for buses could be set strategical-ly on board to determine where congestionimpedes the bus during the peak hour,

■ incorporation of automatic passenger counting todetermine relative priority at an intersection.

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