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83 Description Driveway throat length is the distance from the outer edge of the traveled way of the roadway to the first point along the driveway at which there are conflicting vehicular traffic movements (1). This is the storage length available that is free of conflicts for vehicles entering or leaving a driveway. Tables 61 and 62 follow. Quantitative Analysis Methods NCHRP Report 659: Guide for the Geometric Design of Driveways (1) provides detailed guid- ance on designing throat lengths to provide safe and efficient driveway operations. The HCM6 (2) can be used to estimate 95th percentile queue lengths on the driveway. C H A P T E R 1 9 Driveway Throat Length Source: Photograph provided by the authors. Access Management Technique Performance Trends and Documented Performance Relationships Operations Safety Increase driveway throat length. â Â Â Â Â Â â â â Â Â Â Â Â Table 61. Multimodal operations and safety performance summary.
84 Guide for the Analysis of Multimodal Corridor Access Management Additional Information â¢ Chapters 11, 16, and 17 in this guide. â¢ Access Management Manual, Second ed.: Section 13.7.5. â¢ Access Management Application Guidelines: Chapter 11, Design Guidelines for Driveway Throat Length. â¢ NCHRP Report 659: Guide for the Geometric Design of Driveways. References 1. Gattis, J. L., J. S. Gluck, J. M. Barlow, R. W. Eck, W. F. Hecker, and H. S. Levinson. NCHRP Report 659: Guide for the Geometric Design of Driveways. Transportation Research Board of the National Academies, Washington, D.C., 2010. 2. Highway Capacity Manual: A Guide for Multimodal Mobility Analysis, 6th ed. Transportation Research Board, Washington, D.C., 2016. Mode Operations Safety Provides sufficient space to allow vehicles to enter the site and circulate and, where parking can be directly accessed from the driveway, to wait for vehicles to back out of parking spaces without causing a queue of entering vehicles to back into the pedestrian crossing or roadway (1). Provides sufficient space to store vehicles exiting the site without blocking internal site circulation (1). On multi-lane entrances and exits, provides sufficient space for weaving maneuvers to position for a downstream turn (1). Decreases the chances of a queue of entering vehicles developing that could back into the roadway (1). Gives entering drivers sufficient time to re-orient themselves before encountering conflicting internal site traffic or decision points related to turning or parking (1). On one-way driveways, provides sufficient length to place âDo not Enterâ and âWrong Wayâ signs that drivers can observe and react to in time (1). No documented effect. Decreases the chances of a queue of entering vehicles developing that could back into the pedestrian crossing (1). No documented effect. Decreases the chances of a queue of entering vehicles developing that could back into the bicycle facility or roadway (1). Similar to motor vehicles and trucks, where buses enter a site (e.g., a major shopping center or a transit center) instead of remaining on the roadway. No documented effect beyond that generally observed for motor vehicle traffic. Provides sufficient space to store exiting trucks, buses, and vehicles with trailers without blocking internal site circulation (1). No documented effect beyond that generally observed for motor vehicle traffic. Table 62. General trends associated with increasing driveway throat length.