Guidelines for the Planning and
Deployment of EVP and TSP
Presented by:
Hesham Rakha
Associate Professor, Civil and Environmental Engineering
Director, Center for Sustainable Mobility
Virginia Tech Transportation Institute
Overview
What 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)
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H. Rakha
Overview
What 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
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H. Rakha
Planning
Institutional 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
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H. Rakha
Planning
Pre-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
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H. Rakha
EVP Evaluations
State-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)
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H. Rakha
EVP Evaluations
State-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)
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H. Rakha
EVP Evaluations
State-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
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H. Rakha
EVP Evaluations
State-of-Art Evaluations
Fairhaven Drive
Stopped Correctly
Didn’t Stop
Stopped & Conflict
US Rt 1
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H. Rakha
EV Traffic
Transit Priority Evaluations
Route 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
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H. Rakha
Transit Priority Evaluations
Field 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-tolow levels of congestion.
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H. Rakha
Transit Priority Evaluations
Modeling Evaluation Results
• TSP has no impact on transit vehicle travel times, systemwide 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%.
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H. Rakha
Transit Priority Evaluations
Columbia 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
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H. Rakha
T=0
T=T+1
N
Transit Vehicle Detected?
Y
Y
Priority Provided in
Cycle?
N
Y
Truncate Conflicting Phase
N
N
Y
Other
Calls for Priority on
Conflicting Approaches?
N
Green Displayed > Minimum?`
Subject Approach Green?
Y
N
N
Set to Maximum
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Y
Phase Exceeds
Maximum?
H. Rakha
Subject
Green Requires
Extension?
Y
Extend Phase by 5s
Transit Priority Evaluations
Summary 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
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H. Rakha
Transit Priority Evaluations
Summary Results
Fixed-time
Adaptive
No TSP


TSP


• 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
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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 systemwide dis-benefits if conflicting approaches are heavily
congested.
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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.
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H. Rakha
Implementation Recommendation
Economic 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).
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H. Rakha
Implementation Recommendation
Procurement
• 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
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Implementation Recommendation
System 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
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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.
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