Guidelines for the Planning and Deployment of EVP and TSP

Presented by:Hesham Rakha

Associate Professor, Civil and Environmental EngineeringDirector, Center for Sustainable Mobility

Virginia Tech Transportation Institute

Slide 2 H. Rakha

OverviewWhat is EVP?

• Emergency Vehicle Preemption (EVP) entails:– Preempting a traffic signal controller by

providing a green phase for an emergency vehicle

• Conditional on the absence or completion of pedestrian phases

• May involve either green extension or red truncation• Ignores traffic signal coordination requirements

(maintaining cycle length)

Slide 3 H. Rakha

OverviewWhat is TSP?

• Transit Signal Priority (TSP) entails:– Providing preferential treatment to transit

vehicles to facilitate their flow

• TSP requests may be conditional on:– Absence of a pedestrian phase– Presence of a green interval– Prescribed level of transit vehicle occupancy– Degree of bus lateness– Level of congestion at signalized intersection

Slide 4 H. Rakha

PlanningInstitutional Issues

• Institutional issues include:– Identification of important stakeholders– Assessment of local EVP and TSP needs– Formulation of local EVP and TSP objectives

and requirements– Compile a document that provides a structured

approach to aid in addressing these institutional issues and local needs

Slide 5 H. Rakha

PlanningPre-Deployment Impact Analysis

• Stakeholders should conduct a local impact analysis – Assess the anticipated consequences of

alternative EVP and TSP strategies under consideration

– Consequences may be the impact on traffic flow and vehicular and pedestrian safety

• Empirical analyses and the use of microscopic traffic simulation

– CORSIM, INTEGRATION, VISSIM, Paramics, & AIMSUN2

Slide 6 H. Rakha

EVP EvaluationsState-of-Art Evaluations

• EVP can produce significant savings in emergency vehicle travel times– Response times reduced by

• 14-23% in Denver, Colorado (1978), • 50% in Addison, Texas (BRW, 1997), • 16-23% in Houston, Texas (Traffic Engineers Inc.,

1991)

Slide 7 H. Rakha

EVP EvaluationsState-of-Art Evaluations

• System-wide impacts:– Increase non-EV vehicle delay by less than 3%

along Route 7 (Bullock et al., 1999)– Multiple preemptions result in significant delay

increases (Nelson and Bullock, 2000)– Travel time increases decrease from 12.2%

over normal travel times after 15 minutes to 3% over normal travel times 60 minutes later (McHale and Collura, 2001)

Slide 8 H. Rakha

EVP EvaluationsState-of-Art Evaluations

• Between 1994 and 2000:– More than 643 EV crashes involving one or

more fatalities nation-wide (USDOT, 2002)

• EVP can decrease the number and severity of crashes:– 70% reduction in accident rate at 285 traffic

signals in St. Paul, MN between 1969 and 1976 – Louisell et al. developed a conflict analysis tool

to quantify the likelihood of crashes

Slide 9 H. Rakha

EVP EvaluationsState-of-Art Evaluations

Fairhaven DriveStopped Correctly

Didn’t Stop

Stopped & Conflict

US Rt 1EV Traffic

Slide 10 H. Rakha

Transit Priority EvaluationsRoute 1 Network Configuration

• US Route 1 arterial in Fairfax, Virginia– 8.1 mi over 27 signalized intersections– Total demand of 16,000 veh/peak period– Fixed-time time-of-day signal timings

Slide 11 H. Rakha

Transit Priority EvaluationsField Evaluation Results

• The findings of the field evaluation study are summarized as follows:– The study demonstrated that a WAAS-enabled GPS

receiver is an effective technology in the evaluation of TSP.

– The study found that dwelling times are not affected by TSP operation.

– Green-extension TSP may reduce delay to transit vehicles at intersections (3 to 6% reductions but were not statistically significant).

• The benefits provided by TSP are highly dependent on the level of congestion and can be maximized under moderate-to-low levels of congestion.

Slide 12 H. Rakha

Transit Priority EvaluationsModeling Evaluation Results

• TSP has no impact on transit vehicle travel times, system-wide travel times, and side street queues.

• An increase in Route 1 demand results in increases in system-wide dis-benefits of TSP. – Maximum system-wide increase in delay is minimal (less than

1.37%). • An increase in the side-street demand does not result in

any statistically significant system-wide disbenefits.• An increase in transit vehicle frequency results in

reductions in bus delays by up to 3.20%. – No system-wide benefits are observed when TSP is operated.

• TSP operations are impacted by the location of bus stops:– Near-side bus stops result in a 2.85% increase in delay, – Far-side bus stops result in network-wide delay savings of 1.62%.

Slide 13 H. Rakha

Transit Priority EvaluationsColumbia Pike Network Configuration

• Columbia Pike arterial in Arlington, Virginia– 1.2 mi arterial carrying 26,000 vehicles per day– 16 SCOOT and 5 fixed-time intersections

N

Slide 14 H. Rakha

T=0

Transit Vehicle Detected?

Y

N

T=T+1

Priority Provided in Cycle?

N

Y

Other Calls for Priority on

Conflicting Approaches? Y

N

Subject Approach Green?

Truncate Conflicting Phase

Green Displayed > Minimum?` N Y

N

Subject Green Requires Extension?

Y

N

Extend Phase by 5s Phase Exceeds Maximum?

Set to Maximum

Y

Y

N

Slide 15 H. Rakha

Transit Priority EvaluationsSummary Results

• Impacts on prioritized vehicles:– Delay, stops, fuel consumption, and emission

reductions for all strategies considered– No clear impact on travel time variability

• Impacts on general traffic:– AM peak: Negative impacts due to high congestion at a

few intersections– Midday: Negligible negative impacts as a result of

spare signal capacity– Increasing negative impacts with increasing number of

prioritized buses– Difficult for traffic along prioritized routes to benefit from

priority due to differences in traffic and transit behaviors

Slide 16 H. Rakha

Transit Priority EvaluationsSummary Results

• Effect of adaptive traffic signal control– Transit vehicles: similar benefits under all types of

signal control strategies– General traffic: less negative impacts under adaptive

control as system is able to automatically adjust to temporary queuing or congestion caused by transit priority

No TSP TSP

Fixed-time Adaptive

Slide 17 H. Rakha

TSP General Conclusions

• Rakha and Zhang (2004) concluded the following:– Generally, TSP provides benefits to transit vehicles that

receive priority. – Traffic demand increase results in larger system-wide

dis-benefits.– Bus frequency increase results in larger system-wide

dis-benefits.– Bus arrivals on

• heavily congested approaches may result in system-wide benefits if conflicting approaches are not congested.

• lightly congested approaches may produce significant system-wide dis-benefits if conflicting approaches are heavily congested.

Slide 18 H. Rakha

TSP General Conclusions

– Transit vehicle arrivals during the early phases produce minimum disruptions to the general traffic

– The system-wide benefits of TSP are highly dependent on the optimality of the base signal timings.

– Transit vehicle dwell times at near-side bus stops can have significant system-wide impacts on the potential benefits of TSP.

Slide 19 H. Rakha

Implementation RecommendationEconomic and Financial

• EVP and TSP projects may:– Have short life span, lower upfront costs, and

higher operating costs than traditional physical infrastructure projects

• Traditional B/C may not be appropriate:– Multi criteria analysis should be used

(Leviakangas and Lahesmaa, 2002).

Slide 20 H. Rakha

Implementation RecommendationProcurement

• Identification of system objectives– A clear understanding of the project scope can

reduce future misunderstandings

• RFP preparation– A single integrator should be responsible for

the design, procurement of components, system integration, installation, testing, and user training

Slide 21 H. Rakha

Implementation RecommendationSystem Installation

• These systems have 3 major components:– In-vehicle subsystems

• Emitter, power system, and microprocessor• May also include GPS and APC devices

– Road-side subsystems• Detectors mounted in the vicinity of traffic signals,

microprocessors, and communication systems

– Center subsystems

• Contractor should be responsible for quality control of all subsystems

Slide 22 H. Rakha

References• References:

– Ahn K., Rakha H., and Collura J. (2006), Evaluation of Green Extension Transit Signal Priority Strategies using Portable GPS Receivers, Transportation Research Board 85th Annual Meeting, Washington D.C., CD-ROM [Paper 06-0641].

– Rakha H. and Zhang Y. (2004), Sensitivity Analysis of Transit Signal Priority Impacts on Operation of a Signalized Intersection, Journal of Transportation Engineering, Vol. 130(6), pp. 796-804.

– Dion F., Rakha H., and Zhang Y. (2004), Evaluation of Potential Transit Signal Priority Benefits Along a Fixed-Time Signalized Arterial. Journal of Transportation Engineering, Vol. 130(3), May/June, pp. 294-303.

– Chang J., Collura J., Dion F., and Rakha H. (2003), Evaluation of Service Reliability Impacts of Traffic Signal Priority Strategies for Bus Transit. Transportation Research Record 1841, pp. 23-31.

• Electronic documents: www.filebox.vt.edu/users/hrakha.