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6 Guide for the Geometric Design of Driveways PAR Pedestrian Access Route Pedestrian Access Route A continuous and unobstructed walkway within a pedestrian circu- lation path that provides accessibility. Ped Pedestrian. From the 2003 MUTCD, Section 1A13.55: "a person afoot, in a wheelchair, on skates, or on a skateboard" (2-2). Pork chop (driveway triangular island) Roadway or driveway channelization in the form of a somewhat-triangular island. P-vehicle The passenger car design vehicle as defined by AASHTO. Also includes minivans, pick-up trucks, sport utility vehicles (SUVs), and standard size vans. Rear overhang The distance from the centerline of the rearmost axle to the rear end of the vehicle. Restrictive median A median, such as a raised or depressed median, designed not to be crossed by a motor vehicle except at selected locations. RV Recreational vehicle (e.g., a motor home). Spillback When a situation exists such that the traffic conditions at the subject driveway influence or affect the operation of vehicles in the outside through lane at or in advance of the driveway upstream of the subject driveway. TCD Traffic control devices, including signs, pavement markings, and traffic signals Threshold The edge, dividing line, or boundary where the driveway meets the public roadway. In many cases, this is a line along the curb edge. Throat length The distance from the outer edge of the traveled way of the intersecting roadway to the first point along the driveway at which there are conflicting vehicular traffic movements. Also referred to as the driveway connection depth, driveway reservoir length, driveway stack- ing distance, driveway storage length. Traveled way The portion of the roadway for movement of vehicles, exclusive of shoulders (2-3). TRB Transportation Research Board Wheelbase The distance between the centers of two axles or wheels. Sometimes shown as the length from the front axle to the rear axle. References 2-1. "R105.5 Defined Terms" in Revised Draft Guidelines for Accessible Public Rights-of-Way. http://www.access- (as of Nov. 23, 2005). 2-2. FHWA. Manual on Uniform Traffic Control Devices. Washington, DC (2003) 760 pp. 2-3. AASHTO. A Policy on Geometric Design of Highways and Streets. Washington, DC (2004) p. 305.