Investigation the Effect of Heavy Vehicles on Capacity of Signalized Intersections Based on Bayes' Theorem

© 2014 American Society of Civil Engineers.Heavy vehicles, considering their size and low rate of acceleration and/or deceleration in traffic stream, are responsible for numerous negative effects on other vehicles. As a result, the capacity of signalized intersections declines significantly as the ratio of heavy vehicles in traffic flow is increased. In literature, there are different methods that are used with the goal of determining those negative effects. HR (Headway Ratio) is one of the most frequently used methods amongst all other methods. In this study, HR method was extended by substituting independent probability combinations set of vehicle types for percentage (%) of heavy vehicles in heavy vehicles adjustment factor FHV equation. Also, four independent car-following combinations probability were considered: heavy vehicle following passenger car (H-C), passenger car following heavy vehicle (C-H), passenger car following passenger car (C-C), and heavy vehicle following another heavy vehicle (H-H). Probabilities of occurrence of each combination for percentage (%) of heavy vehicles were calculated by using the Bayes' theorem. The comparisons of results with different studies indicate that there is a significant difference between suggested new model and other studies on high heavy vehicle ratio condition. Moreover, the results showed that the proposed new model may give more accurate results being used in the intersections with high ratio of heavy vehicles