TRAFFIC SIGNAL SETTINGS

A COMPUTER SIMULATION TECHNIQUE WAS USED TO EVALUATE AND TO ASSIST IN DEVELOPING FORMULAS FOR DETERMINING OPTIMUM SIGNAL TIMING, INCLUDING SPLIT AND CYCLE LENGTH CALCULATION. THE FIRST PROBLEM APPROACHED IS THE EVALUATION OF DELAYS AT A SIGNALIZED INTERSECTION. AN APPROXIMATION FORMULA IS PRESENTED TO CALCULATE AVERAGE DELAY PER VEHICLE, ASSUMING RANDOM ARRIVALS. TO CALCULATE GREEN TIME FOR EACH PHASE, ONE INTERSECTION APPROACH FOR THE PHASE IS USED - THE ONE WITH THE HIGHEST RATIO OF FLOW TO SATURATION FLOW. CYCLE LENGTH IS CALCULATED TO MINIMIZE OVERALL DELAY USING A GIVEN FORMULA. A FORMULA, SENSITIVE TO CHANGES IN THE HIGHEST RATIO OF FLOW TO SATURATION FLOW AND THE TOTAL LOST TIME PER CYCLE IN SECONDS, IS PRESENTED TO CALCULATE THE CAPACITY OF THE INTERSECTION. INFORMATION AVAILABLE ON LOST TIME SUGGESTS A VALUE OF ABOUT 2 SECONDS PER PHASE PLUS ANY ALL- RED PERIODS. SATURATION FLOW IS DEFINED AS: WHEN THE GREEN PERIOD COMMENSES, A CERTAIN TIME ELAPSES WHILE VEHICLES ARE ACCELERATING TO NORMAL RUNNING SPEED, BUT AFTER A FEW SECONDS, THE QUEUE DISCHARGES AT A MORE OR LESS CONSTANT RATE. EMPIRICAL DATA WERE DEVELOPED FROM PREVIOUS RESEARCH TASKS AND FROM FIELD STUDIES AT THREE INTERSECTIONS IN THE LONDON AREA FOR THE PURPOSE OF VALIDATING RESULTS AND CALIBRATING THE VARIABLES.