The Development of a Hierarchical Car-following Model of Traffic Behavior on Freeways and Expressways

Several distance thresholds were defined in the car following algorithm namely safety distance, desired following distance, minimum following distance, and catch up distance. These distance thresholds, plus the angular velocity threshold and the relative speed of vehicle to its front vehicle, were used as the measures to classify the situation of vehicle. Seven different possible situations were defined. For each situation, the proper relationship to calculate the required acceleration of vehicle was proposed. A combination of stopping distance and constant deceleration models was used in the car following algorithm. When the vehicle is moving in the merge area, the resulting acceleration rate may be adjusted to reflect drivers desire to facilitate merging. The results of validation of the developed car-following model indicated that there is a good match between the results of the model and real data under similar conditions.