Consistency Evaluation of Interchange Alignments

The concept of design consistency evaluation provides highway designers with a proactive tool for roadway safety improvement. Previous research has focused on the development of evaluation models for basic highway segments, while little research has considered interchange ramps. Interchange ramps differ from major roadways in the complexity of vehicles' acceleration and deceleration activities on them. The objective of this paper is to develop a practical consistency evaluation method for interchange alignments based on the theory of operating speed. To begin with, by giving a profound analysis of the moving characteristic of vehicles on ramps, the speed-change process on ramps is divided into five phases. Next, operating speed along highway ramps and speed differential between successive elements of ramps are calculated based on regression models developed by previous research. Three criterions are then established to evaluate the design consistency of ramp alignments. Lastly, a real life example is presented to illustrate the proposed method.