ASPECTS OF TRAFFIC FLOW ON GRADES

IN THIS PAPER, THE RESULTS OF AN INVESTIGATION INTO TRAFFIC BEAHVIOUR ON GRADES ON RURAL HIGHWAYS IS PRESENTED. BASED UPON OBSERVED PERFORMANCE CHARACTERISTICS OF VARIOUS CLASSES OF VEHICLE, A NUMBER OF VEHICLE PERFORMANCE MODELS ARE DEVELOPED AND CALIBRATED. THESE INCLUDE EXPRESSIONS FOR BUNCHING, SPEED REDUCTION, AND BUNCH AND VEHICLE SPEEDS FOR TRAFFIC IN NO-OVERTAKING ZONES ON LEVEL ROADS. IN ADDITION, DECELERATION MODELS FOR CARS AND TRUCKS ON GRADES ARE DEVELOPED. USING THESE MODELS, SIMULATION TECHNIQUES WERE USED TO ESTABLISH VEHICLE DELAYS ON HILLS IN TERMS OF TRAFFIC VOLUMES, THE PROPORTION OF TRUCKS IN THE TRAFFIC STREAM, THE LENGTH OF GRADE, AND THE GRADIENT. THE SIMULATION MODELS CAN BE USED TO ESTABLISH WARRANTS FOR THE PROVISION OF CLIMBING LANES. THESE WARRANTS CAN BE EXPRESSED EITHER IN ECONOMIC OR IN LEVEL-OF-SERVICE TERMS. AS AN EXAMPLE, CHARTS ARE PRESENTED SHOWING CRITICAL GRADE LENGTHS (IN TERMS OF GRADE, TRAFFIC FLOW AND PROPORTION OF TRUCKS) ABOVE WHICH CLIMBING LANES ARE REQUIRED IN ORDER TO SATISFY ARBITRARY LEVEL-OF-SERVICE CRITERIA. /AUTHOR/