Headway Analysis for Different Combination of Vehicles in a Congested Traffic Flow in freeways

The time headway is an important characteristic of drivers’ behavior and traffic flow, with a great effect on traffic safety, level of service and capacity of transportation systems. In this paper, different groups of the headways are analyzed based on different combination of a pair of leadingfollowing vehicles in a car following situation. Statistics deductions indicate that drivers in car following situations select proper headways based on the type of a specified vehicle and its leading vehicle type. Based on I-80 data, results indicate that there is a significant difference between the headways of different pair of vehicles. When a heavy vehicle follows another one, the headway is the most and headway for groups includes motorcycles and passenger cars which follow a passenger car is the least. In addition, groups include heavy vehicles (a heavy vehicle following a passenger car, a heavy vehicle following another one and a passenger car following a heavy vehicle) have the most headway in comparison to other pair of vehicles. So when heavy vehicles increase in traffic flow, average time headway would also increase. Results of this research can be used for improving microscopic traffic simulation models