PRIORITY TREATMENT OF BUSES AT TRAFFIC SIGNALS

Two basic schemes, passive and active priority, are developed to give buses priority at traffic signals. Passive priority is a signal timing plan for an intersection or a group of intersections which can be changed in several ways to favor buses. Four possible ways are discussed: Adjustment of cycle length; splitting of phases, timing plans, and metering of vehicles. Active priority or preemption occurs when a signal from a bus results in overriding an existing traffic signal pattern, substituting a pattern beneficial to the bus. Two types of preemption are discussed: Unconditional preemption and conditional preemption. Priority for buses at traffic signals has the potential for reducing one of the largest causes of delays on urban artierials. Implementation is relatively easy and can be done at moderate or low cost. Passive priority techniques generally require only engineering and support services and no capital investment. At high levels of demand, bus priority may be disruptive to overall traffic flow. Also, a preemptive system will increase traffic maintenance costs.