Agenda - Council - 06/13/2017 - Laserfiche WebLink

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access off Alpine Drive also provides significant sight distance to the east (left - turning sight distance) with the Puma Street/Alpine Drive intersection being visible from the proposed access location (>850 feet of sight distance). Because it was evident sight distance was not an issue for these movements at the accesses time measurements were not required. However, the Right turning movement from Alpine Drive/Site Access field measurements were taken. This was achieved by standing at the proposed access location and recording time gaps for vehicles traveling eastbound along Alpine Drive. As discussed in the American Association of State Highway and Transportation Officials' (AASHTO) Geometric Design of Highways and Streets, "studies have indicated that a constant value of time gap, independent of approach speed, can be used as a basis for intersection sight distance determinations." Using time gap instead of calculated distances based on the posted speed limit can be more accurate as it accounts for actual speed of the mainline. If drivers routinely travel faster or slower than the speed limit, using time gap captures those true speeds in terms of the impact on sight distance. Measurements were collected and used to determine the average right turn sight distance times. Table 6 shows the required right turn sight distance times for each design vehicles with the average measured sight distance to the west (right -turning sight distance) for Alpine Drive/Site Access. Table 6 — Right Turning Sight Distance Design Vehicle Requirements Passenger Car Single Unit Truck Combination Truck Alpine Drive Access Field Measurement (Average) Right Turn Sight Distance (Seconds) 6.5 8.5 10.5 9.17 As Table 6 shows, there is sufficient sight distance provided at the Alpine Drive/Site Access for right turning Passenger Cars and Single Unit Trucks. Combination Trucks, which require 10.5 seconds of sight distance time to complete a safe right turn movement, are not provided sufficient sight distance at this intersection. This does not raise any concerns however, as the other three access surpass sight distance thresholds. It should be noted that this analysis did not consider modification to Armstrong Boulevard & Bunker Lake Boulevard as the prior Future Business Park Traffic Memorandum completed by Bolton & Menk already defined necessary upgrades for the intersection that would be required for proper traffic flow through the intersection. Traffic Impact Study 11 Capstone Homes Residential Development NSULTING