Spillback from an exit ramp of an expressway.

Discussion is given of the problem of control of an over saturated system comprising an expressway, a highway, and an exit ramp leading from the expressway to the highway. A traffic light is assumed to control the intersection of the exit ramp and the exit highway. When this intersection becomes over saturated, the queue along the ramp may spill back into the mend in the service rate of the exit ramp can be effected at the expense of causing some additional delay to the traffic on the exit highway. The operation of the traffic light serving the intersection of ramp and highway is determined, which minimises the delay of the vehicles served by the entire system.