Modeling vehicle headways for low traffic flows on urban freeways and arterial roadways

One of the important microscopic flow characteristics that affects safety, level of service, driver behavior, and capacity of the roadway is vehicle headway. The time between arrivals of successive vehicles passing a point on roadway is called vehicle headway. This study aims at analyzing the vehicle headway for urban freeway and arterial roadway sections in Riyadh (capital of Saudi Arabia) and comparing them with results from international research. Only low volume traffic conditions is of the concern in this research. The paper describes the mathematical distribution for vehicle headway data on two types of roadways (freeways and arterials). The study found that shifted exponential distribution and gamma distribution appear to reasonably fit data from freeways and atrerials, respectively.