INTERDEPENDENCE OF CERTAIN OPERATIONAL CHARACTERISTICS WITHIN A MOVING TRAFFIC STREAM

THE CONGRESS STREET EXPRESSWAY SURVEILLANCE PROJECT INVESTIGATED THE INTERDEPENDENCE OF CERTAIN FREEWAY OPERATIONAL CHARACTERISTICS WITHIN A MOVING TRAFFIC STREAM BY MEANS OF ELECTRONIC TRAFFIC SURVEILLANCE EQUIPMENT. LANE OCCUPANCY, WHICH IS A POINT MEASUREMENT COMPARABLE WITH CONCENTRATION, WAS COMPARED TO VOLUME AND SPEED, AND THE INTERRELATIONSHIP WAS RECORDED. LANE OCCUPANCY WAS USED TO PREDICT VEHICLE SPEEDS WITH REASONABLE ACCURACY. AERIAL PHOTOGRAPHS WERE USED TO COMPARE OCCUPANCY AND AERIAL DENSITY OF TRAFFIC. THE COMPARISON EMPHASIZED THE CONTRAST BETWEEN POINT MEASUREMENTS AND SECTION MEASUREMENTS. TRAFFIC CONGESTION WAS DISCUSSED AND A POSSIBLE DEFINITION OF CONGESTION WAS DEVELOPED. SPEED INVERSION WAS DESCRIBED. THE VALUE OF VARIOUS MEASURES OF TRAFFIC PERFORMANCE INCLUDING VOLUME, SPEED, SPEED DIFFERENCES, HEADWAYS AND OF VARIATIONS IN INDIVIDUAL SPEEDS, SPEED DIFFERENCES AND HEADWAYS FOR PREDICTING THE ADVENT OF CONGESTION WAS CONSIDERED. THE POSSIBLE REQUIREMENTS OF A TRAFFIC CONTROL SYSTEM /SUCH AS RAMP METERING/ TO CONTROL CONGESTION WERE STUDIED.