The Effect of Vehicle Type on the Saturation Headway at Urban Signalized Intersections

The capacity of an urban signalized intersection is fundamental importance in designing new intersection and modifying existing one. In “Highway Capacity Manual” (HCM) to account the effects of heavy vehicles in the flow at signalized intersections only the proportion of heavy vehicle is considered, queue position of vehicle is not taken into consideration. The presence of taxi in the queue at signalized intersections had significant impact on the saturation headway. For a given number of queue length saturation headway is smaller if proportion of taxi is high. Furthermore, presence of taxi increases the capacity of urban signalized intersections. The presence of small size motorized vehicles (three wheeler auto rickshaws) had a similar positive impact on the capacity of signalized intersections. So, this factor should be considered for designing the signal timing of urban signalized intersections to reduce the congestion. This paper aims at examining the effect of vehicle type (large vehicle, taxi and small size motorized vehicles) on the saturation headway. This paper also aims at developing saturation flow rate adjustment factor for taxi at signalized intersections.