Vehicle Headway Distribution in Work Zones

This study investigates work zone vehicle headway distribution by disaggregating the vehicle headways into four types: car—car, car—truck, truck—car and truck—truck. It first confirms that the four types of vehicle headways are significantly different by performing the Kruskal—Wallis and Mann—Whitney tests using work zone headway data from Singapore. The statistical test results further show that four factors — traffic flow rate, percentage of trucks, work intensity and lane position — have a significant impact on each type of vehicle headway in work zones. A useful methodology is thus proposed to determine the best-fitted headway distribution model for each type, which includes two procedures: determining the best distribution pattern for each type using the maximum-likelihood estimation and Kolmogorov—Smirnov test techniques and formulating the distribution model parameters as a function of the aforementioned four factors.