Influence of On-Ramp Spacing on Traffic Flow on Atlanta Freeway And Arterial Street System

The purpose of this study was to determine the influence of ramp spacing on the traffic flow characteristics on the Atlanta Freeway System and city streets influenced by the freeway. Timelapse photography was used to collect data at four study locations on the freeway. Speed and delay studies were also made on the freeway and surface streets during ramp closure periods and during normal operation of the freeway. Comparisons were made of volumes, speeds, densities, overall travel, and overall travel time on the streets within the system using analysis of variance techniques. It was found that closing any one of the northbound on-ramps on the North Freeway during the afternoon peak hour improved the overall operating characteristics of the freeway. This improvement was shown by a smoother and more uniform flow of traffic as reflected by the speeds and densities on the freeway with none of the ramps_ closed. Closing any one of the northbound on-ramps caused a significant increase in the total travel time in vehicle-minutes within the system. The overall travel in vehicle-miles was not changed significantly by closing any one of the northbound on-ramps within the system . As a result of this study, it was recommended that the Fourteenth Street northbound on-ramp be closed during the afternoon peak period for three months and that further tests be carried out on a system basis to determine if the Fourteenth Street northbound on-ramp should be closed during the peak period on a permanent basis.