Robert D Layton

Balancing Urban Driveway Design Demands Based on Stopping Sight Distance

Many roadways in urban areas, especially dense commercial areas, are subjected to on-street and adjacent off-street parking demands; local access through driveways is an essential component of these complex urban corridors. Vehicles entering and exiting these driveways–-and their interaction with parked cars, other moving motorized vehicles, bicycles, and pedestrians–-present challenges for a safe and efficient roadway corridor. The location and the design of these driveways, together with parking and bicycle facilities, generate sight distance challenges that affect pedestrians and bicyclists. This paper investigates the type and nature of impacts–-including conflicts, sight distance, operations, and safety at driveway locations–-as they relate to pedestrians, bicyclists, and drivers. It also analyzes design geometrics that may help to provide adequate sight distance for safety at driveways with and without bicycle lanes present. Parked vehicles often obstruct drivers’ view of approaching motor vehicles and bicycles. In many locations, vehicles exiting driveways must edge out into the active travel way for the driver to have an unobstructed view. Driveway location and design analysis demonstrate the value of bicycle lanes in providing enhanced sight distance. Current practices permit longitudinal placement of on-street parking too close to driveways. For safety reasons, agencies should consider excluding on-street parking on roads with bicycle lanes when speeds exceed 30 mph so as to provide adequate sight distance without creating sporadic on-street parking spacing. Roads without bicycle lanes often do not provide adequate stopping sight distance at on-street parking driveway locations when motor vehicle operating speeds exceed 25 mph.