Cross-Cutting Findings
Key questions in any effort to deploy an EVP system are, "What are the benefits?" and, "What are the costs?" This section provides an overview of the findings of the cross-cutting study.The Benefits of EVP
The benefits of EVP range across a variety of public interest issues. The benefits realized by the three featured sites are summarized in Figure 8. These benefits include improvements at operational, planning, and economic levels.
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[Specific examples highlighting the benefits are presented below.
Improved Response Time
Fairfax County, Virginia — In nearly all response runs, the system saves anywhere from a few seconds to a few minutes. Station 11 EV drivers cited savings of 30-45 seconds at a single intersection such as the one at U.S. 1 and South Kings Highway (Figure 9).
Figure 9. A Ladder Truck Without EVP Pushes Through a Queue at a Red Signal
Plano, Texas — Plano's need for EVP stems from the combination of the layout of its road network and its traffic signal timing plan. Many of Plano's streets have center medians and narrow shoulders, so that vehicles trying to get out of the way of an EV have no place to go. Therefore, without EVP, it can frequently take two or three cycles to clear an intersection so that the EV may pass. Many of Plano's traffic signals have long cycle lengths of up to 2 or 3 minutes, making it even more important to install EVP at those intersections to reduce clearance time.
Improved Safety
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"The system has had a positive impact on the service we provide to the community." — Captain Lange,
"C" Shift Captain,
Fire and Rescue Station 11 Fairfax County |
Plano, Texas — A study conducted by the City of Plano Risk Management Office indicated that there were 22 EV crashes from 1981 to 1983. Of these 22 crashes, seven occurred at signalized intersections and may have been preventable had EVP been in place. Over the 20 years since the installation of EVP, there have been only four crashes involving emergency vehicles at intersections. In three of these crashes, the cause of the crash was failure of the private vehicle involved to stop for the red signal display correctly generated by the EVP system. The fourth was caused by EV driver error.
St. Paul, Minnesota — In 1977, St. Paul conducted one of the most extensive studies of EVP and EV crash rate reduction available.20 The study documented the rate of EVP deployment across the city's nearly 300 signals and tracked the number of EV crashes and EV responses over the same period. Crashes were reduced from the 1967 high of eight EV crashes to an average of 3.3 EV crashes per year in the latter years of the study. In the report, the fire chief noted that the improvement in crash rates occurred despite an increase in the number of alarm responses and the volume of traffic encountered on the St. Paul roadways. The fire chief indicated that the decrease in the number of EV crashes was due to the dramatic reduction in the conflicts EVs are exposed to at signalized intersections.
Traffic Flow Impacts of EVP
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"The vehicle queues on side-street approaches became slightly longer but would typically clear during the first green phase following the preemption event." — Doug Hansen,
Senior Transportation Planner Fairfax County |
Fairfax County, Virginia — An evaluation of traffic flow impact on U.S. 1, conducted in 2003 by the Virginia Tech Transportation Institute,21 found that the average duration of a preemption event was 25 seconds and that delay impacts on side streets were minor. Backups normally cleared during the first signal cycle following the preemption event.
Plano, Texas — The degree of impact on traffic flow at a particular intersection depends on the frequency of calls made on a particular signal and the level of congestion on the roadway. In Plano, some signals near hospitals often experience multiple preemption calls resulting in queues that take several cycles to clear. During peak periods, it can take 10 to 20 minutes for the traffic flow to return to normal. However, citizen complaints about the impact are few because of high public awareness of the purpose of the system. City engineers pointed out that they get almost immediate cell phone call feedback on malfunctioning signals but get very few calls that can be attributed to the impact of a preemption event.
The Cost of EVP
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"The public is aware of the preemption system and tolerates the inconvenience as part and parcel to the high quality of emergency services they have grown to expect." — Lloyd Neal,
Transportation Engineering Manager, City of Plano |
The cost of EVP systems per intersection and per vehicle vary depending upon the technology selected, the number of units purchased, and the baseline intersection and vehicle conditions. Intersection cost variables include the availability of power on the mast arm or signal suspension cable, the need to run new power and communications cables through existing conduit, and the availability of suitable detector placement locations. Vehicle cost variables include whether or not the vehicle was built with provisions to house the power supply and the emitter and the requirement to develop special brackets to mount the emitter to the vehicle.
Equipment costs, by component, reported by the three sites visited are summarized in Table 6. More information about the costs of emergency vehicle preemption is available from the ITS Costs Database available at http://www.itscosts.its.dot.gov.
| System Component | Capital Cost ($K in 2003 dollars) |
O&M Cost ($K/yr in 2003 dollars) |
|---|---|---|
| Equipment Required per Intersection: | ||
| Signal Preemption Receiver w/ optional confirmation light | 2-3 | 0.25-0.5 |
| Signal Phase Selector | 2-5 | No specific maintenance required |
| Equipment Required per Vehicle: | ||
| Signal Preemption Emitter Note: Initial cost includes a power supply and the emitter (high end of cost range) while maintenance costs primarily entail optical emitter replacement (low end of cost range) |
0.7-2.1 | Remove and replace the optical emitter upon failure |
Fairfax County, Virginia — In Fairfax County, the county is responsible for the cost of equipment purchase and installation on VDOT owned signal systems. Because the Fairfax County deployment involved a retrofit of existing signals, the costs per intersection varied due to a range of signal suspension methods employed along the corridor. Each intersection was surveyed to determine the special design considerations and the impact on the project budget and the deployment schedule. Across seven intersections in the operational test section, the average cost was between $4,000 and $6,000 per intersection (equipping two arterial approaches only).
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"For a site, the structure, and the apparatus, the cost is about $3 million (2004 dollars); and the continuous operations and maintenance costs are about $2.5 million per year for each station." — Bill Peterson Fire Chief, City of Plano |
Fairfax County is responsible for maintenance of the system. The county has employed a maintenance contractor that bills the county directly. As of 2004, experience from the field operational test was being used to develop a county budget line item that will cover the 50 existing or near-term planned EVP intersections. County officials estimated these annual EVP maintenance costs to be between $250 and $500 per year.
Plano, Texas — Plano, Texas does not separate out costs of the EVP system because it is fully integrated into traffic signal operations. However, the traffic engineering department estimates that the cost to install the preemption detection on a new signal at all four approaches is between $5,000 and $8,000 of the $105,000 (or higher) total cost of the signal design, installation, and integration. Differences in cost are dependent upon such factors as the site requirements for power and mast arm installation.
Because Plano owns and operates the EVP systems and the signal systems, the city does not differentiate signal maintenance costs and preemption maintenance costs. EVP maintenance costs are part of the overall signal system maintenance budget. Plano reports that most system failures are traceable to construction and damage to power and signal communications conduits in the vicinity of the intersection.
St. Paul, Minnesota — In the City of St. Paul, the cost of preemption equipment is integral to the cost of new signals. The city estimates the cost of equipping a new traffic signal with preemption capability is approximately $6,000 to $8,000 at all four approaches, provided that the necessary conduits, wiring, and power sources are available.
St. Paul performs regular preventive maintenance on EVP detectors, including lens cleaning and removal of tree overgrowth that prevents the equipment from receiving a preemption call. City maintenance staff trim nearby tree branches and clean the receiver lenses every two years. St. Paul does not differentiate signal maintenance costs and preemption maintenance costs. Both preventive and responsive EVP maintenance are included in the Department of Public Works annual budget.
Potential Cost Savings
Plano, Texas — As part of its 20-year growth plan developed in the mid- 1980s, Plano estimated that one fire/rescue and EMS stations would be required for every 5.6 square miles to provide the desired level of service. As the city grew, the response time benefit of EVP has been incorporated into the geographical information systems (GIS)-based planning models the city uses to evaluate fire/rescue and emergency medical service expansion needs. As a result, the city is now serving 7.5 square miles per station instead of the anticipated 5.6 square miles. The benefit to the city is that it is currently operating 10 stations compared with the 13 that had been forecast resulting in a capital cost savings for the city of approximately $9 million and an annual operating cost savings of approximately $7.5 million.
20 Fire Chief, Department of Fire and Safety Services, St. Paul, Minnesota (1977). Emergency Vehicle Accident Study (Year 1977).
21 McHale, G. and Collura, J. (2003). "Improving Emergency Vehicle Traffic Signal Priority System Assessment Methodologies." Paper presented at the 82nd Annual Meeting of the Transportation Research Board, Washington, D.C. 2003.