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_ Existing Transportation Conditions <br /> <br /> Table 2-2 <br /> Level of Service Definitions <br /> Level of <br /> Service Interpretation V/C Ratio <br /> <br /> A Uncongested operations; all queues clear in a single Less Than 0.60 <br /> signal cycle. <br /> B Very light congestion; an occasional approach phase is 0.60-0.70 <br /> fully utilized. <br /> C Light congestion; occasional backups on critical approach- 0.71-0.80 <br /> es. <br /> D Significant congestion on critical approaches, but intersec- 0.81-0.90 <br /> tion functional. Cars required to wait through more than <br /> one cycle dudng short peaks. No longstanding queues <br /> formed. <br /> E Severe congestion with some long-standing queues on 0.91-0.99 <br /> cdtical approaches. Blockage of intersection may occur if <br />' traffic signal does not provide for protected turning move- <br /> ments. Traffic queue may block nearby intersections(s) <br /> upstream of critical approach(es). <br />' F Total breakdown, stop-and-go operation. 1.00 and Greater <br /> <br /> A signalized intersection's level of service can be calculated with a number of methods. <br /> For this study, a method based on critical movement analysis, called the VCCC method <br /> " was used. VCCC stands for Volume-to-Capacity Contra Costa County. See Appendix A for <br /> a full description of the VCCC program. This method is identical to the Circular 212 <br /> method except that the saturation flow is increased from 1,500 to 1,800 vehicles per hour. <br /> - This adjustment was based on saturation-flow rate studies conducted by CCTA in Contra <br /> Costa County. The volumes of cars on a critical movement are summed and divided by the <br /> capacity of the movement. This V/C ratio of each critical movement at an intersection is <br /> - used to produce an overall intersection V/C ratio also taking into account signal phasing. <br /> The overall V/C ratio is then correlated to a level of service (see Table 2-2). AM peak-hour <br /> and PM peak-hour levels of service are shown by city in Table 2-3. <br /> <br /> Most intersections of routes of regional significance in the Tri-Valley area operate at <br /> LOS D or, better. LOS D is generally considered to be an acceptable operating condition <br /> - for major intersections. All but one intersection meet this criteria in the AM peak hour. <br /> The exception is Vasco/I-580 EB Off-Rnrnp (LOS F). During the PM peak hour three <br /> intersections operate at Level of Service E or F: Vasco/I-580 WB Off, Vasco/I-580 EB Off, <br /> and Danville/Stone Valley. <br /> <br /> -- Barton-Aschrnan Associates, Inc. 25 <br /> <br /> <br />