Vehicular turning and path of travel with a proposed curb bulb on the southwest corner of Mount Diablo Boulevard and Dewing Avenue.

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1 October 3, 2014 James Shively Stantec 100 California Street, Suite 1000, San Francisco CA Subject: Traffic Study for Proposed Lafayette Chase Bank Dear Mr. Shively: Pursuant to your request, Parisi Transportation Consulting (Parisi) has prepared this vehicular path of travel and sight line analysis consistent with the site plan for the proposed development at 3603 Mount Diablo Boulevard in the City of Lafayette, California. The proposed project is a 4,151 square foot (SF) Chase Bank on a vacant site on the southwest corner of Mount Diablo Boulevard and Dewing Avenue. Mount Diablo Boulevard serves as the City s commercial corridor; it is abutted by residential uses to the south and State Route 24 to the north. Opposite Dewing Avenue is a commercial parking lot; the parking lot provides pedestrian access into the Lafayette BART station. Per the City s request, the study addresses the following issues: Vehicular turning and path of travel with a proposed curb bulb on the southwest corner of Mount Diablo Boulevard and Dewing Avenue. Sight distance for the project driveway on Dewing Avenue. Vehicular turning and path of travel analysis The proposed project site plan includes a curb bulb-out at the southwest corner of Mount Diablo Boulevard and Dewing Avenue. Per the City s request, the effects of the curb bulb-out on vehicular turns and path of travel were analyzed for various design vehicles. Industry standard practice uses vehicular turn templates as defined by the American Association of State Highway and Transportation Officials (AASHTO). Figure 1 presents the minimum turning path for passenger car (P) and single unit truck (SU); Figure 2 presents the same for an intermediate semitrailer (WB40). The turns were modeled as initiated from the outside edge of the second westbound lane Bridgeway, Suite B208 Sausalito, CA

2 Project driveway sight line analysis Per the City s request, the project driveway accessing Dewing Avenue was analyzed to determine the necessary sight distance. At an unsignalized intersection, a clear line of sight should be maintained between the driver of a vehicle, bicyclist, or pedestrian waiting at the intersection and the driver on the intersecting roadway. The line of sight should be clear from vertical obstructions like structures, fences, landscape materials and parked vehicles higher than 36 inches. The line of sight from the driveway was measured from the middle of the exiting driveway lane at the sidewalk curb line. This simulates a condition where the driver has partially pulled out of the driveway and into the Dewing Avenue parking zone. The line of sight is measured to the middle of the oncoming lane (five feet offset from the centerline). Table 1 presents the sight distance requirement for various design speeds, and the corresponding length of curb on the west side of Dewing Avenue that should remain clear from vertical obstructions. Table 1: Project Driveway Clear Zone Dewing Avenue No Parking zone (measured from edge of driveway) Stopping sight North of South of Design Speed (mph) distance (ft) 1 driveway (ft) driveway (ft) AASHTO Green Book (2001), Exhibit 3-1. Stopping Sight Distance Please let me know if you have any questions. Sincerely, Andrew Lee, TE Sr. Transportation Engineer cc: David Parisi, PE, TE 2

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