Mathematical modeling of freeway ramp merging capacity analysis based on revised headway distribution model

Determination of merging capacity for a freeway ramp section is important when one analyzes quality of traffic flow at freeway system. It is believed that merging capacity of a freeway ramp merging area can be calculated mostly by analyzing headway distributions of a freeway basic section upstream of freeway ramps. However, because of the fact that headway distribution of the freeway basic section is to change prior to arriving at the ramp segment, the existing method results in an overestimation. In this research, an attempt was made to redefine the headway distribution at a freeway ramp merging area and the refinement accounted for a set of various effects of vehicles merging behaviors on freeway merging capacity calculations. The most distinctive characteristic of the suggested headway distribution is to reflect ramp traffic volumes as one of the parameters for calculating the merging capacity. Gap acceptance model was developed in this procedure for checking the possibility for an entering vehicle within the ramp to merge into freeway main flow. Also mathematical analyses were made to determine the merging capacity for the total traffic flow. It was found that the possible merging capacity must be decided by combining freeway main line flow and ramp flow. Some of merging capacity calculation results produced in this research showed much different values from the ones in the Highway Capacity Manual. This suggests that by using the proposed method more efficient ramp designs and freeway flow managements can be realized. (a) For the covering entry of this conference, please see ITRD abstract no. E214938.