development and evaluation of intelligent bus priority conce

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Transportation Research Record 1727

Paper No. 00-1543

Development and Evaluation of Intelligent Bus Priority Concept

Kevin N. Balke, Conrad L. Dudek, and Thomas Urbanik II

Development and laboratory testing of an intelligent concept for provid-ing priority to buses at signalized intersections without disrupting pro-gression are discussed. The concept used bus position information topredict when in the cycle a bus would arrive at the bus stop and stop lineof a signalized intersection and to determine whether a bus needs prior-ity. The strategy used to provide priority was selected on the basis of theestimated arrival time of the bus at the stop line. Priority was provided byusing phase extension, phase insertion, and early return strategies with-out causing the controller to drop from coordination. Implementation ofthe strategies was accomplished through normal traffic-signal controllercommands (such as Ring Force Offs and Phase Holds). Hardware-in-the-loop simulation studies were performed to evaluate the effectiveness of theconcept with real traffic-signal controllers. The performance of the intel-ligent bus priority approach was examined at three volume-to-capacitylevels: 0.5, 0.8, and 0.95. Signi cant reductions in bus travel times wereachieved at all three volume-to-capacity levels by using the intelligentbus priority approach. Use of the intelligent bus priority approachresulted in only minor increases in total system stop delay and individ-ual approach stop delays at volume-to-capacity levels of 0.5 and 0.8. Theresults of the simulation studies performed as part of this study suggestedto the researchers that the intelligent bus priority approach could be usedat moderate traffic levels (up to volume-to-capacity levels of 0.9 or less)without signi cantly affecting cross-street delays.

Many traffic-signal controllers have bus priority logic already embed-ded in their software. One problem with existing bus priority algo-rithms is that they often use the same strategy to provide priority (e.g.,extend the main-street green or return early to the main-street green)regardless of when in the cycle the bus arrives at the intersection. Insome instances, this can cause nonpriority phases to be either reducedsigni cantly or even skipped altogether, resulting in excessive delaysto the cross street or skipped approaches. Perhaps more importantly,many traffic-signal controllers provide priority by preempting thenormal operation of the traffic signal, causing the signals on an arte-rial to lose coordination. Often, it takes several cycles before coordi-nation between two signalized intersections can be reestablished.During this time, the traffic signals are operating with timing plansthat are less than optimal for traffic conditions. Another problem withmost current bus priority systems is that the controllers do not con-sider whether a bus truly needs priority. Most current systems eitherrely on the bus driver to decide whether priority is warranted or grantpriority to all buses regardless of whether the bus would bene t or isin need of preferential treatment at the intersection. Because of theselimitations, many transportation agencies contend that the effects of

K.N. Balke, TransLink Research Center; C.L. Dudek, Department of Civil Engi-neering, Texas A&M University; and T. Urbanik II, Texas Transportation Institute,Texas A&M University System, 3135 TAMU, College Station, TX 77843-3135.

disrupting progression and the increase in nonpriority delays offsetthe bene ts of providing priority to transit vehicles and are hesitant toimplement bus priority in their jurisdictions.INTELLIGENT BUS PRIORITY CONCEPT

In this study, an “intelligent” bus priority concept was developed toaddress the limitations of the current methods of providing prioritytreatment to buses along an arterial (1). To be “intelligent,” a buspriority system would achieve all of the following design objectives: Provide priority without disrupting progression on the primaryarterial street.

Provide priority without signi cantly altering the normalsequencing and duration of the noncoordinated phases.

Provide priority only to those buses that were truly in need ofpriority on the basis of measurable, user-de ned criteria.

The concept was based on the premise that by tracking the progressof the bus as it travels down an arterial and estimating when in thetraffic-signal cycle the bus would arrive at an intersection, minoradjustments to the timing plans of the signals could be made with-out forcing the signal to preempt its existing operation or severelyaltering the sequencing or duration of the cross-street phases. Toachieve this, an approach that used advanced vehicle tracking, com-munication, and control technologies was developed to perform thefollowing functions:

Estimate the arrival time of the bus at the bus stop and at theintersection, accounting for any stops that the bus may experiencealong the way;

Compute whether the bus is sufficiently behind schedule towarrant priority treatment at the intersection;

Examine different strategies for providing priority to the busand select the one that is most appropriate given where in the cyclethe signal will be when the bus arrives at the intersection; and

Adjust the sequencing or duration of the traffic-signal phases inan “intelligent” manner so that the transit vehicle is given a greenindication when it is ready to proceed through the intersection.Figure 1 illustrates the basic logic of the intelligent bus priorityconcept. Information about the position of the bus as it travels thearterial is used to predict when in the cycle the bus will arrive at thebus stop and at the stop line of the intersection. The travel time ofthe bus from its current location to the bus stop, the dwell time ofthe bus at the bus stop, and the travel time of the bus from the busstop to the interse …… 此处隐藏：4070字，全部文档内容请下载后查看。喜欢就下载吧 ……