Growing traffic volume on the nation's urban highway infrastructure that exhibits limited opportunity for expansion inevitably produces traffic environments that are oversaturated. Oversaturated environments are caused bytraffic demands that exceed available capacity and can produce queues that grow over time. These queues on an urban network can overflow the storage capacity of urban streets and physically block intersections, sharply reducing capacity when most needed. Even when intersection blockage is restrained by costly on-site enforcement, signal control policies designed forundersaturated conditions and based on an objective of minimizing delay and stops can be ineffective and even counterproductive. This paper presents an arterial control policy designed expressly for the oversaturated traffic environment. It is designed to maximize throughput while providing assurance that the intersections are clear of vehicles at signal phase changes (i.e. at the beginning of green). Features of this policy include: (1) Mandates queue spillback as a metering mechanism while ensuring clear intersections when needed; (2) Self-regulating; organically adjusts the metering rate through spillback blockage to compensate for fluctuating, cycle-by-cycle demand and service rates, with no adjustment in control parameters needed; (3) Straightforward application as a fixed time control policy withlimited computational burden, with guidance for real-time application. The control policy is based on an analytical model of the queuing environment and its associated kinematic behavior of traffic. Selected results are presented.
Abstract