Modelling Probability of Breakdown in Interurban Expressways Considering Longitudinal Alignments of a Sag and the Adjacent Sags

Abstract

It is important to reveal a relationship of longitudinal alignment to bottleneck section to consider a mechanism of breakdown phenomena. First, this paper confirms that a ratio of the change of the longitudinal gradient is an appropriately alternative index of the radius of a curvature using traffic counter data and longitudinal alignment data on Tohoku Expressway. Second, a logistic regression model to express break-down in flow is calibrated using traffic flow rate and a ratio of the change of the longitudinal gradient of adjacent sags on Tomei, Kanetsu, Joban as well as Tohoku Expressways. Third, the authors explore alternative models where a ratio of the change of the longitudinal gradient is non-linearly transformed as the transformed ratio has a peak at a specific ratio. When the specific ratio is 0.5%/km, the fitness of the model is the best. This means that a sag whose ratio of the change of the longitudinal gradient at is moderate and whose adjacent sags are sharp, has a tendency to break down to congestion.