FIELD VALIDATION OF INTERSECTION CAPACITY FACTORS

Presented are the results of a series of saturation flow surveys conducted throughout the United States at signalized intersections. The purpose of this research was to verify the saturation flow rates and traffic volume adjustment factors used in various capacity analysis procedures by collecting a relatively extensive data base. Saturation flow headways for more than 20,000 observations were collected for a series of 12 geometric, traffic characteristic, and environmental factors and compared with baseline saturation flow headways for various signal cycle length and phase combinations. Vehicle blockage and lane distribution surveys were conducted for 19,000 additional observations. Based on the results of these surveys, a series of modified adjustment factors is suggested to allow the analyst to determine modified saturation flow rates when calculating signalized capacity.