CHARACTERISTICS OF LEFT-TURNING PASSENGER VEHICLES

GENERAL CHARACTERISTICS OF LEFT-TURNING PASSENGER VEHICLES HAVE PROVED TO BE OF CURRENT INTEREST TO THOSE CONNECTED WITH GEOMETRIC DESIGN. THE STUDY LOCATIONS CHOSEN PROVIDED TWO BASIC CONDITIONS; NAMELY, 90-DEG. ALIGNMENT OF THE VEHICLE TO THE INTERSECTING ROAD, AND A ZERO VEHICULAR SPEED AT THE BEGINNING OF THE TURN. DATA COLLECTION WAS MADE BY A PHOTOGRAPHIC METHOD. BOTH RURAL AND URBAN LOCATIONS WERE CHOSEN FOR THE STUDY. THE WIDER RANGE OF TURNING SPEEDS WAS FOUND TO OCCUR AT THE URBAN LOCATION. THE 85 PERCENTILE VALUE AT THE URBAN LOCATION WAS FOUND TO BE 21.4 MPH, WHILE AT THE RURAL LOCATION THE 85 PERCENTILE VALUE WAS 16.9 MPH. THE MAXIMUM ACCEPTABLE SIDE FRICTION FACTORS DISPLAYED A REFLECTION OF THE SPEED CHARACTERISTICS IN THAT THE FREQUENCY DISTRIBUTION CURVES WERE OF THE SAME GENERAL SHAPE AS THOSE FOR SPEED. A CORRELATION OF TURNING PATHS WITH SPEED GROUPS AT EACH INTERSECTION PROVED THAT THE SHAPE OF THE TURNING PATHS REMAINED APPROXIMATELY CONSTANT FOR SPEED GROUPINGS AT EACH INTERSECTION. THE CHARACTERISTICS OF TRANSVERSE PLACEMENT AT THE BEGINNING AND END OF TURNING MANEUVERS WERE CONSTANT FOR ALL SAMPLES OBSERVED IN THIS STUDY. ANALYSIS REVEALED A CORRELATION BETWEEN TIME AND DISTANCE REQUIRED TO TRAVERSE A TURNING CURVE AND THE SPEED ATTAINED AT THE FINAL TANGENT POINT. IT WAS FOUND THAT HIGHER SPEEDS, MEASURED AT THE FINAL TANGENT POINT, DO NOT DECREASE THE TIME REQUIRED TO TRAVERSE A LEFT TURN. THESE HIGHER SPEEDS DO INCREASE THE TOTAL DISTANCE TRAVELED. THE INCREASED DISTANCE IS NOT EVIDENCED BY AN INCREASED TURNING RADIUS, BUT IT OCCURS THROUGH THE USE OF A LONGER TRANSITIONAL SPIRAL AT THE COMPLETION OF THE TURN. /AUTHOR/