LEVEL OF SERVICE FOR MIXED TRAFFIC FLOW AT SIGNALISED INTERSECTION

Abstract

The concept of level of service (LOS) was first introduced in the 1965 edition of Highway Capacity Manual and was defined as a qualitative measure of the effect of a number of factors, which include speed and travel time, traffic interruptions, freedom to maneuver, safety, driving comfort and operating cost. The concept, as defined, relates solely to measures and characteristics that directly affect the quality of service provided to the driver. The 1965 edition of HCM defined six levels of service for signalised intersections based on load factor, a parameter dependent on the demand volume. After publications of HCM (1965) many researchers have postulated that load factor may not be true indicator of intersection performance and a better para-meter could be average stopped delay caused to individual vehicle (AID). Therefore, delay was included in the HCM (1985) to define Level of Service at Signalised Intersection. Research conducted during the development of HCM (1985) has shown that delay and V/C ratio are not related on a one-to-one fashion. Higher delay may be experienced at low V/C ratio if signal progression is poor. Further, HCM (1985) and other related standards have suggested measurement of delay on lane basis. In India, lane discipline is not strictly followed by road users and-they do not move one after another. iii Due to above and many other problems associated with the measurement and interpretation of delay, an attempt has been made in this study to redefine Level of Service parameters for Signalised Intersection under mixed traffic situations. Degree of saturation, proportion of vehicle required to stop at intersection and probability of cycle failure were consi-dered the appropriate parameters. They are easy to measure in the field and directly related to driver's perception of quality of service provided at intersections. Data collected at eight intersections in Delhi have been analysed and break-points have been determined for various levels of service based on delay and saturated green ratio. iv