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Computational Intelligence and Neuroscience
Volume 2014, Article ID 236072, 7 pages
Research Article

Estimation of Critical Gap Based on Raff’s Definition

1National ITS Center, Research Institute of Highway, Beijing 100088, China
2School of Traffic and Transportation, Dalian Jiaotong University, Dalian 116028, China

Received 26 July 2014; Accepted 5 October 2014; Published 9 November 2014

Academic Editor: Xiaobei Jiang

Copyright © 2014 Rui-jun Guo et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Critical gap is an important parameter used to calculate the capacity and delay of minor road in gap acceptance theory of unsignalized intersections. At an unsignalized intersection with two one-way traffic flows, it is assumed that two events are independent between vehicles’ arrival of major stream and vehicles’ arrival of minor stream. The headways of major stream follow M3 distribution. Based on Raff’s definition of critical gap, two calculation models are derived, which are named M3 definition model and revised Raff’s model. Both models use total rejected coefficient. Different calculation models are compared by simulation and new models are found to be valid. The conclusion reveals that M3 definition model is simple and valid. Revised Raff’s model strictly obeys the definition of Raff’s critical gap and its application field is more extensive than Raff’s model. It can get a more accurate result than the former Raff’s model. The M3 definition model and revised Raff’s model can derive accordant result.