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73 Description A driveway designed and signed to allow either entering or exiting movements, but not both. One-way driveways may be used to support site-circulation needs (e.g., drive-through lanes or fuel pumps), to provide access at a location where only certain movements are suitable, or to support right-in, right-out access to a site (1). Tables 53 and 54 follow. Quantitative Analysis Methods Motor Vehicle Operations Methods in the HCM6 can be used to compare the operations of 2 one-way driveways with that of 1 or 2 two-way driveways (2). Equation 18-3 and Exhibit 18-11 in the HCM6 give the reduction in roadway free-flow speed due to access point density (2). This reduction (in mph) equals â0.078 Da/Nth, where Da is the number of access points per mile (considering both sides of the roadway) and Nth is the number of through lanes in the direction of travel. The resulting increase in average travel speed will be slightly lower, as discussed in the appendix. For an individual site, using 2 one-way drive- ways in lieu of 1 two-way driveway will reduce average travel speeds by a negligible 0.04 mph (4-lane roads) or 0.07 mph (2-lane roads). However, if most accesses along a section of roadway have been designed for one-way operation, the cumulative effect will be more significant. C H A P T E R 1 6 One-Way Driveways Source: Photograph provided by the authors.
74 Guide for the Analysis of Multimodal Corridor Access Management Access Management Technique Performance Trends and Documented Performance Relationships Operations Safety Install 2 one-way driveways in lieu of 1 two-way driveway. â Â â â Â â â â Â Â Â Â Install 2 one-way driveways in lieu of 2 two-way driveways. â Â Â Â Â â â â Â Â Â Provide reversible operation of driveway. Â Â Â Â Â Â Â Â Â Â Require two-way driveway operation where internal circulation not available. Â Â Â Â Â Â Â Â Â Â ÂÂÂ ÂÂÂ Â Table 53. Multimodal operations and safety performance summary. Mode Operations Safety In selected situations (e.g., drive-through lanes or gas stations) can help support internal site circulation (1). If used frequently along a roadway, installing 2 one-way driveways in lieu of 1 two- way driveway will reduce free flow and travel speeds due to the increased number of access points drivers must monitor (2). Requires careful attention to geometric design and signing to minimize intentional and unintentional wrong-way use of driveways (3). Skewed exits require drivers to turn their head sharply to view potential conflicts (4). Skewed entries may encourage higher-speed right-turn maneuvers but may also discourage prohibited left-turn maneuvers. No documented effect. Skewed exits require drivers to turn their head sharply to view potential conflicts (4). Skewed entries may encourage higher-speed right-turn maneuvers. Bicycle LOS decreases when the unsignalized access point frequency on the right side of the road exceeds 20 points per mile. This decrease is partially (or wholly, at traffic speeds less than 25â 30 mph) offset by the decrease in motor vehicle speeds, which positively affects bicycle LOS (2, 5). Skewed exits require drivers to turn their head sharply to view potential conflicts (4). Skewed entries may encourage higher-speed right-turn maneuvers. Similar effects as for motor vehicles. Closely spaced entry and exit driveways may preclude the ability to provide a midblock bus stop at that location. No documented effect beyond that generally observed for motor vehicle traffic. No documented effect beyond that generally observed for motor vehicle traffic. No documented effect beyond that generally observed for motor vehicle traffic. Table 54. General trends associated with installing one-way driveways. Motor Vehicle Safety Section 13.8 in the Access Management Manual (3) provides guidance on designing one-way driveways to encourage proper driver use. Bicycle Operations Equations 18-41 and 18-44 in the HCM6 (2) can determine the effect of motorized vehicle speeds on bicycle LOS, while Equations 18-46 and 18-47 can determine the effect of unsignalized access spacing on bicycle LOS. For an individual site on a suburban arterial, using 2 one-way
One-Way Driveways 75 driveways in lieu of 1 two-way driveway will reduce the bicycle LOS by no more than 0.01 point, where 0.75 points represents the range covered by one LOS letter. If most accesses along a section of roadway have been designed for one-way operation, the cumulative effect will be more significant. Additional Information ⢠Chapters 1, 11, 15, and 17 in this guide. ⢠Access Management Manual, Second ed.: Section 13.8. ⢠Access Management Application Guidelines: Section 10.5.4. ⢠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. Highway Capacity Manual: A Guide for Multimodal Mobility Analysis, 6th ed. Transportation Research Board, Washington, D.C., 2016. 3. 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. 4. 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. 5. 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.
