The operational and safety effects of lane width are combined with those of other cross sectional elements. Knowledge of the total effects of lane width, shoulder width, and the roadside offers insights into mitigation when less than desirable lane widths may be necessary. The operational and safety effects of lane width are combined with those of other cross sectional elements. Knowledge of the total effects of lane width, shoulder width, and the roadside offers insights into mitigation when less than desirable lane widths may be necessary.
On two-lane rural highways, the total roadway width (lanes and shoulders) influences crash frequency. The quality of the roadside (slope, clear zone), in combination with the roadway, influences both the severity and frequency of crashes. Mitigation measures for narrow lanes on rural roads may thus include wider shoulders and improved roadsides. Indeed, designers should avoid design solutions that provide wider lanes at the expense of the roadside and/or shoulder. Such solutions may actually result in a net degradation in safety; as a minimum, they may be costly with little or no actual benefit. This is particularly the case for lower volume roads, on which the predominant crash type is run-off-road and highway capacity is not a major consideration. Where narrower lanes are used, designers should consider lane widening at sharp horizontal curves. Special attention to centerline and edge line delineation and, except where bicycling is likely, the use of shoulder rumble strips to alert drivers are also mitigation measures appropriate for two-lane roads with narrow lane widths. Improved stopping sight distance (SSD) should also be considered as a mitigation measure.
For urban streets and highways, the mitigation of narrow lanes should focus on operational impacts or similar problems. Flush or raised medians should be considered where narrow lanes are used for four- or six-lane urban arterials.
Source: A Guide for Achieving Flexibility in Highway Design p. 65
Published: 2004
From A Guide for Achieving Flexibility in Highway Design, 2004, by the American Association of State Highway and Transportation Officials, Washington, D.C. Used by permission. AASHTO publications may be purchased from that organization’s bookstore at 1-800-231-3475 or online at https://bookstore.transportation.org.
