Entering Headway for Through Movements at Urban Signalized Intersections

When vehicles in a queue start crossing a stop line (or any other reference line) at a signalized intersection after the signal turns green, the entering headway (discharge headway) is the time that elapses between consecutive vehicles. This headway is a factor in determining intersection capacity. The current study aims at analyzing the entering headway at selected signalized intersections in Riyadh (the capital of Saudi Arabia). It is unlikely that driver behavior is similar in different countries, and therefore it is unwise to use the values for headway times from other countries to fit traffic conditions in Saudi Arabia. To date, no research of this type has been conducted in Saudi Arabia. This study attempts to investigate the entering headway at intersections in Riyadh and to compare the results with corresponding results from international research. Eight signalized intersections (with two-lane and three-lane approaches) along eight major streets in Riyadh were selected for study. A total of 720 single-lane traffic platoons entering the intersections were observed. It was found that the average entering headways for Vehicles 1 through 15 at two-lane intersections in Riyadh after the light turned green were 3.23, 2.41, 2.29, 2.1, 2.02, 1.84, 1.72, 1.64, 1.53, 1.68, 1.58, 1.31, 1.13, 1.19, and 1.01 s. For the three-lane sites the headways for Vehicles 1 through 13 were as follows: 3.37, 2.23, 2.03, 1.92, 1.81, 1.81, 1.72, 1.69, 1.6, 1.48, 1.37, 1.33, and 1.46 s. The study found that the saturation flow rates were 2,293 and 2,195 vehicles/hour of green per lane for two-lane and three-lane sites, respectively. These intersection approaches appear to have higher saturation flow rates than those in previous studies from other countries.