Reso 2018-2806 - Laserfiche WebLink

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miamt-vaae county,i-L. tswyuiz-Mizu - The goal of both priority and preemption is to give preferential treatment for requesting vehicle on the appropriate intersection movement. However, the methods to accomplish that preference are quite different as described below. • Priority: Signal priority typically implies that the controller delays, or extends, traffic signal phase transitions so that a vehicle arrives at the intersection in the green interval of the desired phase. The request for priority may or may not be granted based on the priority of the request and the current traffic situation at the intersection. The controller does not differentiate between a transit vehicle that is on schedule, behind schedule or ahead of schedule and relies on the driver to enable or disable the in-vehicle transmitter requesting the priority. A priority request will give preference to the requested movement, but with no guarantee of a green light. Finally, preference in signal priority is given with a goal to minimize the disruption to signal operation, particularly in coordination. • Preemption:Signal preemption, as the name suggests, is a more brute force method of giving preference to the requestor. In this case, the current operation is "preempted"and phases can be shortened, extended, or even omitted (with the exception of pedestrian clearances)to provide a green interval on the requested movement. Even in the case of preemption, however, there are no guarantees as the request can be trumped by higher priority and/or conflicting preemption requests, or the vehicle may arrive before the controller can safely cycle to the requested movement. Finally, preemption is typically provided with little or no regard for signal operation, and is nearly always followed by a transition to return to coordination. In both cases, the optimized traffic patterns and traffic flow are negatively impacted when either vehicle priority or preemption request is served, resulting in additional total vehicle delay and increased stops as well as fuel consumption. To mitigate these negative impacts as well as expand the total foot print to all traffic signals under Centracs control, this Task is structured to satisfy the following objectives: 1. Expand the preemption/priority coverage using centralized strategies without the addition of expensive local intersection hardware. 2. Minimize the impact of preemption and priority through the following strategies: • Priority will be granted to only those transit vehicles that are running behind schedule as reported by the transit system minimizing the overall impact from the occurrences of unnecessary priority calls. Depending on the capability of the transit system, behind notifications could also be coupled with input from the passenger counters, etc. •Vehicle priority will be granted for emergency vehicles and/or transit vehicles on a route basis through center-to-center communications, not intersection-by-intersection. The sooner the controller can be informed of a potential priority request; the more time is available to shorten or lengthen phases to serve the vehicle using priority versus preemption. • Emergency vehicles will receive a preemption when priority cannot satisfy the request. 3. Stakeholders shall experience the following benefits: • Traffic— Enhanced management or preemption calls • Transit— Improved on time performance • Emergency services—Enhanced response times To accomplish these objectives, this Task is organized into three phases with the ability to modify successive phases based on the outcomes of the prior phase. Page 41 of 57