MINI-COMPUTER CONTROLS RAMPS

THE PRIMARY OBJECTIVE OF RAMP METERING IS TO LIMIT THE TRAFFIC ENTERING A FREEWAY SO THAT DEMAND WILL NOT EXCEED THE CAPACITY OF THE FREEWAY SECTION IMMEDIATELY DOWNSTREAM. A TRAFFIC SIGNAL ON THE RAMP SET TO RELEASE VEHICLES ONTO THE FREEWAY AT A PREDETERMINED RATE PREVENTS TRAFFIC FROM ATTEMPTING TO ENTER THE ROADWAY. FREE-FLOWING TRAFFIC ON THE FREEWAY IS THUS RESTORED, ALTHOUGH DELAYS AND QUEUES MAY OCCUR ON THE RAMP. THIS DELAY WILL DIVERT SOME MOTORISTS TO POINTS FARTHER ALONG THE FREEWAY WHERE FREE-FLOW ACCESS IS AVAILABLE. IT ALSO DISCOURAGES THE USE OF THE FREEWAY FOR SHORT TRIPS WHEN THERE IS ADEQUATE CAPACITY ON LOCAL CITY STREETS. HOWEVER, THIS REQUIRES THAT ALTERNATE ROUTES, OTHER MODES OF TRANSPORTATION, OR OPTIONAL TRIP TIMES BE AVAILABLE. CURRENT RAMP-METERING SYSTEMS OPERATE ON A FIXED-TIME CONTROLLER AND DO NOT CORRELATE CONDITIONS ON ONE RAMP OR FREEWAY SECTION WITH CONDITIONS ON OTHERS. THE CALIFORNIA DIVISION OF HIGHWAYS HAS INSTALLED A TRAFFIC- RESPONSIVE METERING SYSTEM AT TWO INTERCHANGES ON U.S. 101 IN SAN JOSE AND RELATED IT TO TRAFFIC ON THE ADJACENT FREEWAY SECTION THROUGH INDUCTIVE LOOP DETECTORS PLACED IN THE FREEWAY LANES. THE SYSTEM IS CAPABLE OF HANDLING UP TO 16 SEPARATE RAMPS. WHEN THE SYSTEM BECOMES OPERATIONAL IT WILL DETECT UNUSED CAPACITY AND OTHER NONRECURRENT INCIDENTS DOWNSTREAM IN THE FREEWAY LANES, WHILE THE LOOPS IN THE RAMPS SENSE THE PRESENCE, PASSAGE, AND DEMAND OF THE VEHICLES AT THE RAMP SIGNALS.