Signal Timing Under Saturated Conditions

A FHWA publication provides guidance to practitioners on effective strategies to mitigate the effects of congestion at signalised intersections.

The scope is limited to single intersections and does not address network-level strategies. The strategies are defined in terms of their underlying objective.

Under congested conditions, traditional objectives and performance measures shift from progression and minimising delay to maximising throughput and managing queues.

Experts were interviewed to identify the strategies and tactics they used to address congested intersections, a discussion of their methods is presented. Select strategies were studied further, particularly the belief that longer cycles are more efficient, and the effects of buses on signal timing in grid networks.

The research revealed that long cycle lengths may not be more efficient at intersections where long queues starve turn lanes. In grid networks, the cycle length that is just long enough to reliably serve busses from a near-side stop was found through simulation to prevent the development of residual queues.

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