AN ANALYSIS OF SHORT-TERM IMPLEMENTATION OF RAMP CONTROL ON THE DAN RYAN EXPRESSWAY

A RAMP METERING STUDY WAS CONDUCTED ON THE NORTHBOUND DAN RYAN EXPRESSWAY TO GAIN KNOWLEDGE OF RELATIVE EFFECTS OF VARIOUS GEOMETRIC DESIGN FEATURES ON RAMP CONTROL. AN INTERPLAY BETWEEN THE EXPRESSWAY AND FRONTAGE STREET RESULTED IN THE GENERATION OF EXCEEDINGLY HIGH ENTRANCE RAMP DEMANDS AT THE POINT WHERE THE EXPRESSWAY CURVES AWAY FROM THE FRONTAGE STREET. RAMP CONTROL, IN THE FORM OF ONE-VEHICLE-AT-A-TIME METERING UTILIZING MANUALLY-OPERATED PORTABLE EQUIPMENT, WAS USED ON FOUR SUCCESSIVE ENTRANCE RAMPS TO ADJUST MERGE DEMANDS TO A LEVEL THAT COULD BE ACCOMMODATED. CONTROL OF THE FOUR ENTRANCE RAMPS DID NOT ELIMINATE CONGESTION, BUT SIGNIFICANTLY REDUCED THE EXTENT AND DURATION. THE SEVERITY OF CONGESTION WAS REDUCED SUCH THAT INDIVIDUAL MOTORISTS SAVED UP TO 5 MINUTES IN TRAVERSING THE 3.6-MILE STUDY SECTION. A DAILY AVERAGE OF 627 VEHICLE HOURS OF EXPRESSWAY TRAVEL TIME WAS SAVED DURING CONTROL, WHILE THE PEAK-PERIOD VEHICLE-MILES OF EXPRESSWAY TRAVEL INCREASED BY 5 PERCENT. DELAYS INCURRED WERE AT THE EXPENSE OF VEHICLES WAITING IN QUEUES AT THE CONTROLLED RAMPS. THERE WAS NEGLIGIBLE DELAY TO SURFACE STREET TRAFFIC IN THE CORRIDOR. RAMP METERING AT THE FOUR RAMPS DID NOT PRODUCE ENOUGH DIVERSION TO DOWNSTREAM RAMPS AND/OR SURFACE STREET ROUTES TO COMPLETELY PREVENT EXPRESSWAY OVERLOADING FROM OCCURRING IN THE STUDY SECTION, BUT SHIFTED THE POINT OF INITIAL OVERLOADING UPSTREAM. THE STUDY POINTS OUT THE NEED TO EXTEND CONTROL TO ADDITIONAL UPSTREAM ENTRANCE RAMPS AND TO ADJUST THE LEVEL OF CONTROL ON A TRAFFIC-ACTUATED BASIS IN ORDER TO FURTHER IMPROVE EXPRESSWAY OPERATIONS.