Conduct rigorous testing prior to deployment of an emergency preemption system to avoid potential problems and negative system impacts.
The experience of multiple agencies with emergency vehicle preemption systems.
Fairfax County,Virginia,United States; Plano,Texas,United States; St. Paul,Minnesota,United States
However, each EVP system needs to be tailored to fit the needs of the jurisdiction. Due to differences in traffic signal controllers and traffic signal systems, an EVP system is not simply a "plug and play" type system. During system installation, adjustments will need to be made prior to system-wide deployment. The system will need to be debugged using the parameters for that jurisdiction and, because of the nature of deploying this type of system and exposing the traveling public and the emergency vehicle to potential conflicts, a field test should be performed before system-wide deployment.
Interviews conducted at the three jurisdictions provide the following guidance for an EVP system installation:
- Bench test the equipment and software in the shop with the same equipment that is found in the field. Bench testing can help prevent potential problems that may occur in the field when the system is deployed. Traffic controllers should be set up in the shop the same way as in the field to replicate any issues that may occur. In Fairfax County, the Virginia Department of Transportation (VDOT) found that their traffic signal controller software required an upgrade to allow dual use of the technology for both EVP and transit signal priority. If provided, transit signal priority should always be a secondary request to an emergency vehicle preemption request. Prior to the software upgrade, VDOT found that the transit priority requests were granted the same level of precedence as an EVP request. If this situation had not been tested before deploying the system in the field, a serious situation may have occurred.
- Wire the vehicle emitter into the EV parking brake or transmission lever to turn the emitter off when the EV is stopped. When an emergency vehicle stops in the vicinity of an intersection, a continuously running emitter will hold the signal in the preemption phase indefinitely, possibly causing significant traffic problems. Preemption systems usually include factory-installed emitters that include a power interrupt tied to the transmission shift lever that disables the emitter when the vehicle is in "park." In both Fairfax County, Virginia and Plano, Texas the technicians had to develop custom power interrupt solutions for vehicles with locally-installed emitters.
- Maintain an open line of communication among stakeholders during the acceptance testing period to avoid poor system performance and perhaps avert a dangerous situation. Resolving system performance issues requires cooperation and communication between EV drivers and EVP maintenance technicians. Certain signalized intersections may pose problems in terms of emitter-detector line-of-sight reducing detection ranges. Finding the right solution requires detailed problem descriptions. The EV drivers need to be involved when the system is being installed and should continue to communicate to technicians any problems in order to maintain optimum system performance. In some cases the maintenance technicians may work for the traffic engineering department and in other cases the technicians may belong to the emergency service department. In either case, it is important that good communication is maintained to provide a high level of system performance and to avoid any possible dangerous situations.
Author: William C. Louisell, SAIC
Published By: Prepared by the FHWA USDOT
Source Date: January 2006
EDL Number: 14097
Other Reference Number: Report No. FHWA-JPO-05-010URL: http://ntl.bts.gov/lib/jpodocs/repts_te/14097.htm
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Lesson of the Month for December, 2006 !
Major Initiatives > Cooperative Intersection Collision Avoidance Systems
Major Initiatives > Mobility Services for All Americans
Major Initiatives > Integrated Corridor Management Systems
Major Initiatives > Emergency Transportation Operations
Major Initiatives > Vehicle Infrastructure Integration (VII)
Other Program Activities > Public Safety
Other Program Activities > Rural ITS Deployment
preempt, emergency preemption, traffic signals, EVP