Two-Stage Gap Acceptance: Some Clarifications

Chapter 17 of the HCM 2000 provides a method for analyzing a two-stage priority process at unsignalized intersections, which provide a wide median in the major street. In the HCM itself, the method is, however, described rather briefly. This could give rise to misunderstandings, and practitioners might avoid using the procedure altogether. This being so, the analytical background of the procedure and the correct application of the parameters will be explained in greater detail. Moreover, graphical representations have been developed to replace the difficult formulas, simplifying application in the field. With these graphs, application becomes significantly easier. The method also has some limitations, which should be taken into account in practical application. Thus, this paper is something like a comment on the method described in the HCM 2000, besides providing some enhancements which allow easier application in practice.