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56 Description Raised islands at the entrance to a driveway and medians within a driveway can be used to separate conflicting motorists, provide positive guidance to motorists, discourage prohibited turns, provide pedestrian refuge, reduce excessive pavement area, or facilitate a combination of these uses (1). Tables 40 and 41 follow. Quantitative Analysis Methods NCHRP Report 659: Guide for the Geometric Design of Driveways (1) provides detailed guid- ance on designing driveway channelization. Potts et al. (3) developed a model for predicting the frequency of vehicleâpedestrian crashes associated with a signalized intersection approach. The model indicates that a channelized right-turn lane at a traffic signal has a similar crash rate as the situation with no turn lane and a lower crash rate relative to an unchannelized right-turn lane. It is unknown whether the same relationships hold at unsignalized intersections. See the appendix for more details about the model. C H A P T E R 1 1 Driveway Channelization Source: Photograph provided by the authors.
Access Management Technique Performance Trends and Documented Performance Relationships Operations Safety Install channelizing island to move ingress merge point laterally away from roadway. Â Â Â â Â â â Â Â â Move sidewalkâdriveway crossing laterally away from roadway. Â Â Â Â Â â â Â Â â Install 2 two-way driveways with limited turns in lieu of 1 full-access two-way driveway. Â Â Â â Â â â â Â â Â Install 2 two-way driveways with limited turns in lieu of 2 full-access two-way driveways. Â Â Â Â Â â â â Â â Â Install channelizing island to prevent left-turn driveway encroachment conflicts. Â Â Â â Â â â Â Â â Install channelizing island to prevent right-turn ingress vehicles from returning to through lanes. Â Â Â â Â â â Â Â â Install channelizing island to control the merge area of right-turn ingress vehicles. 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 Â Â Â Â Â Note: â = unchanged performance. Table 40. Multimodal operations and safety performance summary. Mode Operations Safety No direct effect. See Chapters 1 and 7. Raised medians in the driveway help separate opposing traffic flows and prevent encroachments (1). Islands help separate right- and left-turning traffic entering driveways with multiple entry lanes. Setback pedestrian crossings allow drivers to exit traffic stream before having to stop for pedestrians (1, 2). Flatter right-turn entry angle imposed by an island requires drivers to turn their heads at a sharper angle to observe approaching traffic and may encourage higher exiting speeds (1). Islands used to discourage prohibited turns are easy to violate if not accompanied by a sufficiently long median barrier (1). Islands that are too small do not stand out and may pose a traffic hazard (1). No direct effect. See Chapters 1 and 7. Sufficiently wide pedestrian refuges and islands provide pedestrian refuge, particularly on higher-volume driveways with multi-lane entries or exits (1). Islands can help discourage prohibited left-turn movements. See Chapters 1 and 7. No direct effect. See Chapters 1 and 7. Islands can help discourage prohibited left-turn movements. See Chapters 1 and 7. Wider driveway widths at the point of intersection with the street will require that a midblock bus stop, if present, be located farther away from pedestrian facilities serving the site located along the driveway. No documented effect beyond that generally observed for motor vehicle, pedestrian, and truck traffic. No documented effect. Channelization must accommodate the turning path of larger vehicles to avoid curb, pavement, and vehicle damage (1). Table 41. General trends associated with driveway channelization.
58 Guide for the Analysis of Multimodal Corridor Access Management Additional Information ⢠Chapters 1, 2, 5, 7, 10, and 17 in this guide. ⢠Access Management Manual, Second ed.: Sections 13.7.6 and 20.2.6. ⢠Access Management Application Guidelines: Chapter 10, Driveway Design and Geometrics. ⢠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, Washing- ton, D.C., 2010. 2. 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. 3. Potts, I. B., D. W. Harwood, K. M. Bauer, D. K. Gilmore, J. M. Hutton, D. J. Torbic, J. F. Ringert, A. Daleiden, and J. M. Barlow. NCHRP Web-Only Document 208: Design Guidance for Channelized Right-Turn Lanes. Transpor- tation Research Board of the National Academies, Washington, D.C., July 2011.
