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Capital Hill PUD Traffic Safety Analysis (14-020) March 3, 2017 2.1.3 Sight Distance The existing driveway intersections on Capital Drive are located between Cresta De Ruta Street and the end near Hendricks Park. All of the existing four site driveways are planned to be retained to continue to serve current residences on the site in their existing function and capacity, while two of them will be reutilized as a looped connection through the site to provide access and circulation for the proposed new development and parcel frontages. Driveway intersection sight distance was measured in the field at the two existing site driveways that will provide access to new development on the site and at the proposed new access within the apex area of the curve that will serve proposed lots 19 and 20. Recommended intersection sight distances based on the American Association of State Highway and Transportation Officials' (AASHTO's) A Policy on Geometric Design of Highways and Streets, (611 Edition-2011) are calculated from the following equation: ISD = 1.47Vmajortq Where: ISD= Intersection Sight Distance = the length of visible roadway (long leg of the sight triangle) along the major road (ft) as measured from the departing driver's observation point 14.5 feet back from the near edge of the traveled way at an assumed driver's eye height and object height of 3.50 feet above the road surface Vmajo, = design speed of major road in mph tg =time gap (seconds) for departing driveway vehicle to enter the major road The time gap is assumed to be 7.5 seconds for a stopped passenger vehicle to turn left onto a two-lane highway with no median and 6.5 seconds for a stopped passenger vehicle to turn right into the nearest travel lane or cross the intersecting street. The time gap is considered the shortest acceptable gap in the traffic stream that a driver in the departing vehicle is willing to accept when maneuvering from the driveway (minor approach) onto the roadway (major approach) and accelerating to design traffic speed. The assumed time gap is adjusted for minor street approach upgrades exceeding three percent by adding or subtracting 0.2 seconds for each percent grade. The time gap may also be adjusted for the number of lanes crossed when a roadway has multiple travel lanes per direction by adding 0.5 seconds for each additional lane crossed (one lane per direction is assumed in the default time gap value). The existing site driveway intersections do not require adjustments to increase the time gap since they are not located on uphill approaching minor street grades and since departing maneuvers do not cross more than one lane of travel. Based on the statutory speed of 25 MPH and rounding up to the nearest five-foot increment, the calculated AASHTO recommended intersection sight distance would be 240 feet when looking to the left and 280 feet when looking to the right (ISD based on left turns for sight distance to the right and right turn/crossing maneuver when looking to the left). AASHTO recommendations are based on typical gap acceptance where a departing vehicle is entering a stream of traffic, and it is implied that there are a significant number of other road users on the major road approach. The street character, function, and associated relatively low traffic volumes on Capital Drive justify a reduced acceptable intersection sight distance as will be demonstrated later. The available intersection sight distance at the northernmost site driveway on Capital Drive was measured at 230 feet when looking to the right with the planned street improvements and vegetation removal within the right-of-way and 168 feet when looking to the left. Figures 2 and 2A in Appendix B depict the existing driveway location and measured available intersection sight © Branch Engineering, Inc. Page 14