RAMP CONTROL TO RELIEVE FREEWAY CONGESTION CAUSED BY TRAFFIC DISTURBANCES

SYSTEMS HAVE BEEN INSTALLED IN SEVERAL CITIES IN THE UNITED STATES, INCLUDING LOS ANGELES, WHICH ALLOW THE CONTROL OF RAMP SIGNAL LIGHTS FROM A CENTRAL LOCATION. TIME-OF-DAY RAMP VOLUME SCHEDULES HAVE BEEN USED WITH SOME SUCCESS. THIS PAPER EXAMINES A CLASS OF TRAFFIC-RESPONSIVE RAMP CONTROL ALGORITHMS FOR ADJUSTING RAMP VOLUMES IN RESPONSE TO TRAFFIC DISTURBANCES, E.G., CONGESTION RESULTING FROM LANE BLOCKAGES. A LARGE NUMBER OF TRAFFIC-RESPONSIVE RAMP CONTROL PLANS ARE CONSIDERED. EACH PLAN IS EVALUATED IN TERMS OF FREEWAY SERVICE (VEHICLE-MILES) AND DELAY (VEHICLE-HOURS) OVER A FIXED CONTROL PERIOD BY SIMULATING THE RESPONSE OF TRAFFIC TO A LANE BLOCKAGE ON A MACROSCOPIC MODEL OF FREEWAY TRAFFIC. THE RESULT OF THE ANALYSIS IS A SET OF RAMP CONTROL PLANS, EACH OF WHICH YIELDS MINIMUM DELAY FOR A SPECIFIED LEVEL OF FREEWAY SERVICE. THE PERFORMANCE MEASURES ASSOCIATED WITH THESE PLANS ARE PLOTTED AGAINST ONE ANOTHER, YIELDING A TRADE-OFF CURVE FOR FINAL SELECTION OF A RAMP METERING PLAN.