# Guide for the Analysis of Multimodal Corridor Access Management(2018)

## Chapter: Chapter 18 - Driveway Vertical Geometry

« Previous: Chapter 17 - Driveway Width
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Suggested Citation:"Chapter 18 - Driveway Vertical Geometry." National Academies of Sciences, Engineering, and Medicine. 2018. Guide for the Analysis of Multimodal Corridor Access Management. Washington, DC: The National Academies Press. doi: 10.17226/25342.
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Page 81
Suggested Citation:"Chapter 18 - Driveway Vertical Geometry." National Academies of Sciences, Engineering, and Medicine. 2018. Guide for the Analysis of Multimodal Corridor Access Management. Washington, DC: The National Academies Press. doi: 10.17226/25342.
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Page 82
Suggested Citation:"Chapter 18 - Driveway Vertical Geometry." National Academies of Sciences, Engineering, and Medicine. 2018. Guide for the Analysis of Multimodal Corridor Access Management. Washington, DC: The National Academies Press. doi: 10.17226/25342.
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Driveway Vertical Geometry 81 Access Management Technique Performance Trends and Documented Performance Relationships Operations Safety Improve driveway vertical geometry. â Â â Â Â Â â Â â Â Â Table 58. Multimodal operations and safety performance summary. Mode Operations Safety Motor vehicles enter the driveway slightly faster (i.e., at a normal entering speed) (3). Reduces vehicle and roadway damage from scraping caused by too-severe changes in grade rate (2). Allows vehicles to enter and exit the roadway at the design speed produced by the horizontal geometry, thereby reducing the speed differential of vehicles on the roadway (4, 5). Improves sight distance between the egressing vehicle and the approaching vehicle. Where the sidewalk is adjacent to the curb, helps achieve conformance with Americans with Disabilities Act requirements for the maximum cross-slope of the pedestrian access route (5). Vehicle speeds increase slightly, but potential vehicleâ pedestrian conflicts still take place at low speeds (3). Improves sight distance between the egressing vehicle and the approaching pedestrian. No documented effect. Removes the potential for abrupt changes in pavement cross slope or elevation (e.g., bumps) that could cause a bicyclist to lose balance or control (3). Vehicle speeds increase slightly, but potential vehicleâbicycle conflicts still take place at low speeds. Improves sight distance between the egressing vehicle and the approaching cyclist. No documented effect beyond that generally observed for motor vehicle traffic. No documented effect beyond that generally observed for motor vehicle traffic. Improves sight distance between the egressing vehicle and the approaching bus. No documented effect beyond that generally observed for motor vehicle traffic. No documented effect beyond that generally observed for motor vehicle traffic. Improves sight distance between the egressing vehicle and the approaching truck. Table 59. General trends associated with improving driveway vertical geometry. Average Speed (mph) by Location and Type of Turn Driveway Grade Prior to Driveway Entering Driveway 15 Feet into Driveway Right Turn Left Turn Right Turn Left Turn Right Turn Left Turn Flatter 14.1 10.3 5.5 10.5 7.2 10.0 Moderate 14.7 10.0 5.8 10.2 7.2 9.5 Steeper 14.5 9.6 5.1 8.7 5.9 8.1 Note: Prior to driveway = 25 feet prior for right turns and 1 lane width prior for left turns; entering driveway = 2 feet beyond driveway threshold. Grade categories: flatter = 1.5%â5.0%, moderate = 6.0%â9.0%, and steeper = 12.5%â15.5%. Source: NCHRP Web-Only Document 151 (3). Table 60. Comparisons of speeds of vehicles entering driveways with differing grades.

82 Guide for the Analysis of Multimodal Corridor Access Management Motor Vehicle Safety NCHRP Report 659 (5) recommends a maximum grade break without a vertical curve of 10% for crests and 9% for sags and as low as 7% for driveways where vehicles towing trailers would be common, based on measurements of 31 driveways with scrape marks. When a driveway slopes downward from the roadway edge [e.g., a downward-sloping drive- way on the outside (or âhighâ side) of a superelevated roadway], sight distance for the motorist exiting the driveway may be restricted because the driveway is pointing upward and the vehicleâs structure restricts the motoristâs view of traffic (i.e., pedestrian, bicycle, transit, and truck) on the roadway (6). Reducing the driveway slope or providing a flatter landing area may improve sight distance. Additional Information â¢ Chapters 17 and 19 in this guide. â¢ Access Management Manual, Second ed.: Section 13.7.7. â¢ Access Management Application Guidelines: Chapter 10, Driveway Design and Geometrics. â¢ NCHRP Report 659: Guide for the Geometric Design of Driveways. References 1. Dixon, K. K., R. D. Layton, M. Butorac, P. Ryus, J. L. Gattis, L. Brown, and D. Huntington. Access Management Application Guidelines. Transportation Research Board, Washington, D.C., 2016. 2. 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. 3. Gattis, J. L., J. S. Gluck, J. M. Barlow, R. W. Eck, W. F. Hecker, and H. S. Levinson. NCHRP Web-Only Document 151: Geometric Design of Driveways. Transportation Research Board of the National Academies, Washington, D.C., July 2009. 4. Layton, R., G. Hodgson, and K. Hunter-Zaworski. Pedestrian and Bicyclist Impacts of Access Management. Proceedings of the Third National Access Management Conference, Fort Lauderdale, Fla., 1998. 5. 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. 6. Florida Department of Transportation. Driveway Information Guide. Florida Department of Transportation, Tallahassee, Sept. 26, 2008.

Next: Chapter 19 - Driveway Throat Length »
Guide for the Analysis of Multimodal Corridor Access Management Get This Book
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TRB’s National Cooperative Highway Research Program (NCHRP) Research Report 900: Guide for the Analysis of Multimodal Corridor Access Management describes operational and safety relationships between access management techniques and the automobile, pedestrian, bicycle, public transit, and truck modes. This report may help assist in the selection of alternative access management techniques based on the safety and operation performance of each affected travel mode.The roadway system must accommodate many types of users—bicyclists, passenger cars, pedestrians, transit, and trucks. This report examines the interactions between multimodal operations and access management techniques and treatments, and the trade-off decisions that are necessary.

NCHRP Web-Only Document 256, the contractor's report, accompanies this report.

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