Emergency Vehicle Preemption

Transcription

1 Emergency Vehicle Preemption Brian Willham, PE, PTOE Traffic Engineer November 18, 2014

2 Emergency Vehicle Preemption is a type of system that allows the normal operation of traffic signals to be preempted in the path of an emergency response vehicle, halting conflicting traffic and allowing the emergency vehicle right-ofway, helping to reduce response times and enhancing traffic safety. Motorists not looking around when they have a green light Some FD s won t enter intersections on red light Can result in dramatic reduction of response time (potentially reducing the need for new stations)

3 Effect on Signal Timing Replaces normal timing and logic with preemptive timing and logic Extends the green time on an approach up to a preemptive maximum, that is irrespective of the maximum green or coordination settings Preemptive service is followed by a recovery or transition period where the controller transitions to normal signal operations and coordination timing plans (if applicable) Transition Into Preemption Yellow & All-Red clearance interval shall not be shortened or omitted Pedestrian walk or clearance intervals may be shortened or omitted A return to the previous steady green signal indication shall be permitted following a steady yellow signal indication in the same signal face, omitting the red clearance interval. Transition out of Preemption Yellow & All-Red vehicle clearance interval of the preempted approach shall not be shortened or omitted A signal indication sequence from a steady yellow signal indication to a steady green signal indication shall not be permitted.

4 Optical / Infrared Preemption Systems Strobe emitting equipment on the vehicle communicates with detector units at signalized intersections that identifies the approach direction of the approaching vehicle and preempts that direction of travel. Relies on visible line of sight Requires a detector for each approach direction (can use a one or two-direction detector units) Detectors need to be near the center of the approach (usually out on a mast arm) TOMAR STROBECOM II

5 Siren Activated Preemption Systems Microphones at the signalized intersections recognize sirens on emergency vehicles to identify the approach direction of the vehicle and preempts that direction of travel. Relies on visible line of sight for the sound of the siren to be detected Requires a detector for each approach direction No additional equipment required for the vehicle TRAFFIC SYSTEMS SONEM 2000

6 GPS / Radio Preemption Systems GPS/Radio unit on the vehicle communicates with signalized intersections to identify the speed, approach direction, and location of the approaching vehicle. The intersection equipment is pre-programmed with an approach map (or zone) to define corridors for priority control. Once the vehicle enters the zone, the controller brings up the green light to clear the intersection prior to the vehicle getting to the intersection Requires only one detector per intersection System is tied into the vehicles turn signals to clear out downstream intersections Can be controlled from inside a fire station to pre-empt near-by signalized intersections GTT OPTICOM GPS

7 Hard Wire Preemption Systems Signalized intersections in close proximity to fire stations can be preempted with a push-button located within the station that is hard wired to the intersection. The preemption can be programmed to engage a certain amount of time after the button is pushed, allowing time for the vehicles to exit the station and enter traffic. Requires conduit/wire from fire station to intersection No equipment necessary for vehicles

8 Active Fire Station Warning Signs Can be used in conjunction with EVP to help alert traffic and minimize blocked exits Hard Wire Preemption Blinker Signs Activate with Preemption

9 Preemption System Selection Many factors to consider when choosing a system Cost Initial costs vs. maintenance costs/time Compatibility Existing systems / Shared Services Corridor Geometry Raised medians / closely spaced intersections Central Management Software Functionality of various systems Planning / Funding Corridor Prioritization (Crash rates / Traffic Volumes / Etc) Add to standard specs Local CIP Funding Fire Grants Traffic Safety Funding (Equipment)