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70 Description Driveway sight distance considers (1): ⢠Stopping sight distance, the sight distance required for a driver to perceive and react to a hazard, and then brake to a stop prior to the hazard; ⢠Intersection sight distance, the sight distance required for drivers exiting an access connection or making a left turn into an access connection to safely make the maneuver; and ⢠Decision sight distance, the sight distance required for drivers to ascertain and safely respond to an unexpected, difficult, or unfamiliar situation, such as finding the access connection serving a business they have not previously visited. Tables 51 and 52 follow. Quantitative Analysis Methods Motor Vehicle Safety AASHTOâs Green Book (5) provides guidance on selecting appropriate values for stopping, intersection, and design sight distance. Pedestrian Operations Equations 18-32 and 18-33 in the HCM6 (3) can determine the effect of parking reduction on pedestrian link LOS. A decrease in the curb length with occupied parking of 10 percentage C H A P T E R 1 5 Driveway Sight Distance Source: Photograph provided by the authors.
Driveway Sight Distance 71 pointsâwith 6-foot sidewalks, no landscape buffer, and standard lane widthsâreduces the pedestrian LOS score by 0.06â0.12 points, with 0.75 points representing the range covered by one LOS letter. Bicycle Operations Equations 18-41 and 18-42 in the HCM6 (3) can determine the effect of reduced parking on bicycle link LOS. A decrease in the curb length with occupied parking of 10 percentage points improves the bicycle LOS score by 0.02 to 0.38 points, with 0.75 points representing the range covered by one LOS letter, with lower reductions at higher percentages of occupied parking. Mode Operations Safety Improved decision sight distance and driveway conspicuity may result in reduced motorist hesitancy. Intersection sight distance provides sufficient distance for drivers to see and react appropriately to potential conflicts (2). Improved decision sight distance and driveway conspicuity may result in fewer erratic maneuvers by drivers. Removing some on-street parking to improve intersection sight distance slightly decreases pedestrian LOS because parked cars serve as a barrier between traffic and pedestrians on the sidewalk (3, 4). Provides sufficient distance for drivers to see and react appropriately to pedestrians crossing or about to cross the driveway (2). Removing some on-street parking to improve intersection sight distance slightly improves bicycle LOS (3, 4). Provides sufficient distance for drivers to see and react appropriately to bicyclists crossing or about to cross the driveway (2). Improving intersection sight distance may require relocating an adjacent bus stop (1). No documented effect beyond that generally observed for motor vehicle and pedestrian traffic. No documented effect beyond that generally observed for motor vehicle traffic. No documented effect beyond that generally observed for motor vehicle traffic. Table 52. General trends associated with improving driveway sight distance. Access Management Technique Performance Trends and Documented Performance Relationships Operations Safety Regulate minimum sight distance. â Â Â Â Â â â â Â Â Improve driveway sight distance. â Â Â â Â â â â Â Â Restrict on-street parking next to driveways. â â â Â Â â â â Â Â Â Â Install visual cues for driveway. â Â Â Â Â â â â Â Â Optimize sight distance in permit authorization stage. â Â Â Â Â â â â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Table 51. Multimodal operations and safety performance summary.
72 Guide for the Analysis of Multimodal Corridor Access Management Additional Information ⢠Chapters 13, 16, and 17 in this guide. ⢠Access Management Manual, Second ed.: Sections 13.4.2 and 13.4.3. ⢠Access Management Application Guidelines: Chapter 10, Driveway Design and Geometrics. References 1. Williams, K. M., V. G. Stover, K. K. Dixon, and P. Demosthenes. Access Management Manual, Second ed. Transportation Research Board of the National Academies, Washington, D.C., 2014. 2. 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. 3. Highway Capacity Manual: A Guide for Multimodal Mobility Analysis, 6th ed. Transportation Research Board, Washington, D.C., 2016. 4. Dowling, R., D. Reinke, A. Flannery, P. Ryus, M. Vandehey, T. Petritsch, B. Landis, N. Rouphail, and J. Bonneson. NCHRP Report 616: Multimodal Level of Service Analysis for Urban Streets. Transportation Research Board of the National Academies, Washington, D.C., 2008. 5. American Association of State Highway and Transportation Officials. A Policy on Geometric Design of Highways and Streets, 6th ed. American Association of State Highway and Transportation Officials. Washington, D.C., 2011.
