Traffic Signal Priority Request

The RAPID Traffic Signal Priority component detects when a bus is running late and sends instructions to traffic lights at intersections along the route to vary the timing of the lights so that the bus is given priority. Within reasonable limits, this allows the bus to regain lost time. For many customers the benefits attributable to the bus priority measures alone outweigh the cost of the entire system.

This bus priority is achieved as follows:

• If the bus arrival time at the intersection is within a predefined window of the expected arrival time then the bus is eligible for priority. This can be set to ensure that buses running ahead of schedule do not get priority
• The priority component conducts a dialogue with the traffic control system for the intersection where priority is to be applied. This dialogue checks to see if the intersection is able to give priority based on a set of rules such as outstanding requests and if the intersection is running in isolated mode. If the priority determination rules are satisfied then priority is requested. If not the request is dropped. All requests are time stamped and logged for later reporting. This interface is fully developed and is operating with the SCATS traffic control system as used in the USA, Australia, across Asia and at over 80 other cities.

Priority measures implemented include:

• Not making a priority call if the intersection reports that it is congested
• Not making a priority call when there is sufficient time remaining in the phase for the bus to get through
• Requesting an extension of the current phase if appropriate and it was going to terminate
• Advancing a phase if appropriate to enable priority earlier

As soon as a bus is detected passing through an intersection the priority call will be cancelled.

The RAPID bus priority solution does not require any changes to be made to the traffic signal controllers or to the traffic control system where these are linked. Existing phases are mapped and those phases that will satisfy a priority call are defined for each service that uses that intersection. Traffic signal engineers may create additional traffic signal priority phases if they wish and these can be mapped similar to normal phases, however this is not required.

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