ANALYSIS OF SIGNALS DELAY AND LEVEL OF SERVICE CONCEPT

An analysis was made of traffic signal delay and the level of service concept. The findings were as follows: (1) Delay was found to decrease with increase in number of lanes and increase in lane width, and to increase with increasing percent of heavy vehicles. (2) The minimum delay cycle length for a given approach depends on the volume/capacity (v/c) ratio. With increase in v/c a higher cycle length is obtained as optimum. (3) Various delay models were reviewed. An interesting comparison was conducted by Akcelik, which found that the Highway Capacity Manual (HCM) delay model overestimated the delay for oversaturated condition (v/c greater than 1.0) as compared to the Australian and the Canadian methods. (4) From a comparison of the HCM model to the Webster equation it was found that the Webster equation gave higher values of total delay than the HCM equation. The Webster model, however, estimated total delay including acceleration and deceleration delays whereas the HCM model estimated only the stopped delay. (5) It is proposed that the level of service of a signalized intersection be characterized as a three dimensional concept. The parameters to be considered are the Quality of Progression and the Saturation Ratio in addition to the delay. A table and several graphs for this concept are presented.