Off-ramp area congestion and off-ramp queue spill over are wide-spread reasons for expressway traffic jams in China.A control strategy was developed to reduce the number of collisions between expressway and surface street vehicles and to reduce spill over by controlling the surface street vehicles to improve the traffic conditions near expressway off-ramps.This control algorithm monitors the traffic conditions at the off-ramp using occupancy rates and a performance index for the surface street vehicles,and then optimizes the control signal split and cycle length for the surface street vehicles assuming that the off-ramp queue is shorter than the minimum allowable length.Simulations indicate improvements in the traffic flow with the average vehicle travel time nearly 10% less and the off-ramp queue reduced significantly.
