Investigating the Relation between Level of Service and Volume-to-Capacity ratio at Signalized Intersections under Heterogeneous Traffic Condition

Among the various performance measures for assessing the operational condition of signalized intersection, both volume-to-capacity (v/c) ratio and control delay have gained importance universally. Even though delay is used as the service measure for arriving at the level of service (LOS) of signalized intersection, the practitioners use v/c ratio as the prime indicator of intersection performance. This study aims at understanding the significance of using the v/c ratio as an indicator of signalized intersection performance under Indian context. Previous studies and various highway capacity manuals have proposed a one-to-one relationship between delay and v/c ratio. The relationship has been revisited to find out whether there is a one-to-one correspondence. Further, an attempt was made to investigate the relationship between level of service and the v/c ratio at signalized intersection under heterogeneous traffic condition. The delay model proposed in the Indian Highway Capacity Manual (Indo-HCM) has been used for this. The results show that the delay distribution under different degrees of saturation are overlapping and it is difficult to arrive at v/c thresholds for each LOS category. i.e. there is no one-to-one correspondence between v/c ratio and delay values. Based on the study results, some approximate thresholds of v/c ratios are proposed for LOS of signalized intersections under heterogeneous traffic condition.