Citation

Cima BT. Transp. Res. Rec. 1977; 630: 44-51.

Copyright

(Copyright © 1977, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

The traffic-conflict technique was modified to evaluate the relative safety of freeway merging with and without the use of entrance ramp-metering control. Six types of traffic conflicts were defined for the entrance ramp and acceleration lane: braking on ramp, braking for lead vehicle, weaving around lead vehicle, entering second lane, entering side by side, and entering late. Five conflicts were specified for the freeway lane (merge lane) adjacent to the acceleration lane; weaving around entering vehicle, braking for entering vehicle, weaving around lead and entering vehicles, braking for lead entering vehicles, and avoiding encroaching vehicles. A three-level severity rating (routine, moderate, and serious) was also developed to assess the seriousness of each conflict. An existing ramp-metering control installation was investigated during freeway levels of service C and D. A two-way analysis of variance was performed on the traffic-conflict data by using, as the independent variables, ramp-control condition (on and off) and freeway level of service (C and D). The study revealed a significant reduction of 11.6 percent in all traffic conflicts when ramp control was activated. Analysis results indicate that acceleration-lane conflicts significantly decreased when ramp-metering control was used. Merge-lane conflicts were found to be related more to freeway level of service than to ramp control. However, merge-lane, multiple-vehicle conflicts and their severity decreased when ramp control was in effect. An analysis of accident records supported these conclusions.