75C - PH - BRISTOL EIR FROM WARNER TO ST. ANDREW

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I DKS Associates The ICU method of analyzing intersection operations is one of several parallel methods j developed in the last two decades that allows the traffic engineer to perform a simple calculation of operating conditions at a signalized intersection. The end result, the overall intersection capacity utilization, is defined as the sum of the ratios of approach volume divided by approach capacity for each leg of intersection which controls overall traffic signal timing plus an allowance for clearance times. Thus, an ICU value of 1.00 corresponds to a condition where the sum of the approach volumes controlling the signal exactly equals the sum of the approach capacities servicing these volumes. The method requires data related to the following intersection characteristics: • Approach lane geometries and capacities, • Turning movement volumes, and • Signal control characteristics. The first data requirement pertains to intersection geometry and driver characteristics. It is necessary to determine the number of lanes available on each approach to the intersection, which turning movements utilize each intersection, and the number of vehicles per hour of green time that a particular lane can carry. This last value is heavily dependent on driver behavior, and has been shown to range from 1,500 -1,800 vehicles per hour of green time. The analysis contained in this report is based on a capacity of 1,600 vehicles per hour of green time for through lanes and 1,500 for turn lanes. The traffic volumes used in ICU analysis can be either actual traffic volumes counted under existing conditions, or projections of existing volumes combined with expected traffic generated by new development in the area. Both types of traffic volumes are analyzed in this report. Finally, the ICU analysis assumes that the signal at an intersection is ideally timed for the approaching traffic volumes. It is thus possible to have an acceptable ICU value and have one or more approaches to the intersection experience poor operations because of signal timing problems. The ICU method does not take interactions with other nearby intersections into account either, so queues from nearby congested locations can also lead to a situation where the ICU calculation indicates acceptable conditions, while severe congestion occurs as a result of interactions with other Iocations. Once all of the necessary information has been assembled, the actual ICU analysis consists of determining the volume -to- capacity (V /C) ratio for each signal phase /approach and summing the individual ratios_ To arrive at the overall ICU, a clearance lost time will be finally added to the calculated V/C ratio. A clearance lost time of 0.02 has been considered in this analysis. Table 3 -3 provides a detailed explanation of level of service for signalized intersections. 28657.P90223xOJRpi 14 75C -546