Gap Acceptance and Traffic Interaction in the Freeway Merging Process. Volume 3. Operational Effects of Some Entrance Ramp Geometrics on Freeway Merging

摘要

Volume 3 of the final report, which consists of seven volumes and a summary report, is an evaluation of the effects of the acceleration lane length, angle of convergence and ramp grade on traffic interaction in the freeway merging process. Field data were collected at 29 entrance ramps located in different parts of the country. The acceleration lanes of the ramps studied ranged from 240 to 1500 feet in length and the convergence angles ranged from 1 degree to 14 degrees. Data were collected using a technique involving time lapse photography from a circling airplane. A regression analysis is presented to determine the factors which affect the use of acceleration lanes as described by the distance from the physical nose to the merge point. The following tentative conclusions are offered: Narrow acceleration lanes (less than 12 feet) have an adverse effect on merging operations. On each of the ramps for which the convergence angle was 3 degrees or less the operation was extremely good. At each of the entrance ramps which had convergence angles 10 degrees or greater and/or an acceleration lane length less than 350 feet very poor operation was noted. On the downgrade ramps which were studied, the operation was much better than would have been expected based on acceleration lane length and convergence angle only. (Author)