SU0004094 - Laserfiche WebLink

Home Browse Search

4.Environmental Analysis Existing traffic volumes were determined by performing manual turning movement counts at each of the project intersections.2 The manual turning movement counts were performed in December and January. A seasonal adjustment factor was applied to account for summer peak traffic. Existing peak-hour turning movement volumes at the study intersections are presented in _ Figures 13 and 14 contained in Appendix C. Traffic volumes on freeways and freeway ramps were determined by reviewing data presented in previous environmental impact reports,data available on the Caltrans web site, and balancing with existing traffic counts on State Route 132. In addition to manual turning movement counts,24-hour machine counts were performed at various locations.The results of the counts are presented in Appendix C. The results of the counts verify the assumption that PM peak-hour analyses are not required for the project. Track traffic originating from the existing mining sites in the project area was determined to be _ negligible during the PM peak hour of the adjacent roads relative to the AM peak-hour volumes. Existing Levels of Service The concepts of capacity and level of service(LOS)are central to the analysis of all traffic facilities,although their meanings and the criteria are different for intersections and roadways, and differ between signalized and unsignalized intersections. At unsignalized intersections, "Stop"or"Yield"signs are used to assign the right-of-way to one street while controlling movements from the other street(s). This forces drivers on the controlled street to select gaps in the major street flow through which they can enter and turn into the intersection, or cross entirely through the intersection. In analyzing the ability of traffic to use gaps in the major street flows,it is generally recognized that certain"critical' movements(i.e., a traffic movement that requires crossing a conflicting traffic stream)are more able to use these gaps than others. A right turn from the minor street — represents the critical movement most able to use available gaps since the driver has to be concerned with gaps in only one direction of major street traffic. A left turn from the major street is the next critical movement most able to use available gaps, followed by through movements and left turns from the minor street. Drivers making left turns from the minor street onto a major two-way street must recognize and negotiate their way through gaps in two directions of major street flows. This concept is important because it highlights the frequent capacity shortages for vehicles seeking to make left turns from a minor street onto a major street. Key input data required to analyze unsignalized intersections include geometric characteristics and peak-hour volumes. Geometric characteristics incorporated into the analysis include the number and use of lanes, lane markings,turn radii,approach angles,and sight distances. Six _ levels of service(with corresponding ranges of average vehicle delay)have been established, from LOS A(little or no delay)to LOS F(very long delays). Level of service characteristics for unsignalized intersections are defined in the 2000 Highway Capacity Manual published by the _ Transportation Research Board and are presented in Table 4.4-1. 2 The counts were perforated by the independent traffic-counting firm of Southland Car Counters(under contract with Peters Engineering Group). RMC Pacific Vernalis Quarry Mining and Reclamation Project 4.4-6 ESA 1203015 Draft Environmental Impact Report May 2006