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TRAFFIC SIGNAL SETTINGS
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1958
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Traffic TheoryEngineeringTraffic FlowAerospace EngineeringAssuming Random ArrivalsComputer EngineeringTraffic Signal SettingsSystems EngineeringTransportation EngineeringThe IntersectionTraffic ModelTraffic EngineeringTraffic Signal ControlTraffic SimulationRoad Traffic ControlSignal ProcessingIntersection Approach
Saturation flow is the rate at which vehicles discharge from a queue once the green phase has been running long enough to reach a steady state. The study aims to derive formulas for estimating average vehicle delay and intersection capacity based on traffic flow ratios and lost time. A computer‑simulation framework evaluates delays, computes green times from the approach with the highest flow‑to‑saturation ratio, and selects cycle lengths that minimize overall delay, with empirical data from London intersections used for validation. Lost time is approximately 2 s per phase plus all‑red periods, and the simulation‑derived formulas were validated against empirical data from three London intersections.
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.