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Abstract
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Two parameters of traffic performance are investigated. They are starting delay and time spacing of vehicles entering a signalized intersection. Time spacing is the average time headway in seconds between successive vehicles in an entering platoon. Time spacing agrees with the definition presented in the traffic engineering handbook in its discussion of traffic signal timing formulas.
CONCLUSIONS drawn with respect to starting delay are: (1) there is a significant difference in starting delay among approaches at different intersections and among different approaches to the same intersection, (2) starting delay on one weekday can be considered equal to starting for all weekdays, (3) factors which influence starting delay and are responsible for the difference in delay among various locations have not been isolated and identified in this study, and (4) starting delays are in most cases normally distributed. Time spacing conclusions are: (1) average time spacing is significantly different for different intersections, but the mean value obtained for one weekday will not usually differ significantly from that for other weekdays, (2) although normality was not tested for all cases, time spacing appears generally to be normally distributed, and (3) time spacing on a given approach appears to be primarily a function of street width and parking conditions for the intersections studied. The maximum capacity of an intersection approach is related to delay and spacing and can be calculated using a given formula. Because of relatively large percentage variation in values from cycle to cycle, delay and spacing are concluded to be of limited value in determination of optimum signal timing. |