A model of freeway merging is developed based on driver behavior. The model proposes that a ramp driver accepts a gap based on the first order motion vectors of an approaching vehicle, which perceptually is angular velocity. This function simultaneously accounts for relative velocity and distance separation. The total model includes driver behavior on the ramp, steering control onto and on the speed change lane, acceleration, gap search, and an abort zone. The model was tested on 102 merges on both a curved ramp and a tangent connector to the speed change lane. The results indicated that an angular velocity model did explain the merge decision point and that drivers used an angular velocity threshold criterion. Using the model, it waspossible to estimate the speed change lane length necessary for theramp driver to find an acceptable gap 85 percent of the time. This length increased with decreasing ramp design speed, but decreased with increasing volume. In general, a speed change lane length of 800 ft is sufficient to ensure an acceptable gap 85 percent of the time for all freeway volumes over 1, 200 passenger cars/lane/hour and rampdesign speeds over 30 mph, assuming an acceleration capability of the ramp vehicle of greater than 1.5 Ft/sq sec. This paper appears intransportation research record no. 1213, Human performance and highway visibility:design, safety, and methods.
Abstract