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Engineering Countermeasures for Roadway Departure Crashes 7 Volume 3 of the NCHRP Report 500 series discusses strategies for addressing collisions with trees in hazardous locations (5). The report presents two objectives for addressing this problem: (1) prevent trees from growing in hazardous locations, and (2) eliminate the hazardous condi- tion and/or reduce the severity of the crash. A âhazardous conditionâ is not explicitly defined in the guide, but it would likely include any area within the required clear zone for the road type, along the roadside within a horizontal curve section, or any location where there is a cluster of run-off-road crashes. The strategies for addressing these two objectives are found in Table 2. Objective Strategies Keep vehicles from encroaching on the roadside Install rumble strips Install edge-line âprofile marking,â edge-line rumble strips, or modify with narrow or no paved shoulders Install mid-lane rumble strips Provide enhanced shoulder or in-lane delineation and marking for sharp curves Provide improved highway geometry for horizontal curves Provide enhanced pavement markings Provide skid-resistant pavement surfaces Apply shoulder treatments: â¢ Eliminate shoulder drop-offs â¢ Widen and/or pave shoulders Minimize likelihood of crashing into object or overturning if vehicle travels off the shoulder Design safer slopes and ditches Remove/relocate objects in hazardous locations Delineate trees or utility poles with retroreflective tape Reduce the severity of a crash Improve design of roadside hardware Improve design and application of barrier and attenuation systems Table 1. Run-off-road objectives and strategies (7). Objective Strategies Prevent trees from growing in hazardous locations Develop, revise, and implement planting guidelines to prevent placing trees in hazardous locations Mowing and vegetation control guidelines Eliminate hazardous condition and/or reduce severity of a crash Remove trees in hazardous locations Shield motorists from striking trees Modify roadside clear zone in vicinity of trees Delineate trees in hazardous locations Table 2. Objectives and strategies for addressing crashes with trees in hazardous locations (5).
8 Practices for Preventing Roadway Departures Volume 4 of the NCHRP Report 500 series discusses strategies and countermeasures for addressing head-on collisions. A head-on crash typically occurs when a vehicle crosses a center- line or a median and crashes into a vehicle traveling in the opposite direction. As stated in the Volume 4 guide, the objectives of reducing the number of head-on fatal crashes are to: â¢ Keep vehicles from encroaching into the opposite lane, â¢ Minimize the likelihood of a car crashing into an oncoming vehicle, and â¢ Reduce the severity of crashes that occur. The strategies (also considered as countermeasures) suggested in that guide for these three objectives are shown in Table 3. FHWA Office of Safety The FHWAâs Office of Safety maintains a website that provides a wealth of information on all aspects of highway safety (8). Its comprehensive program, in part, focuses on three areas that have been identified as providing the greatest potential to reduce highway fatalities using infrastructure-oriented improvements: roadway departures, intersection crashes, and pedestrian/bicycle crashes. As noted earlier, roadway departure crashes alone account for over 50% of the fatalities, are related with intersections for another 4.4%, and are related with pedestrian/bicyclist crashes for 1.3%. A section of the website is devoted to roadway departure safety (1). In that section, the FHWA notes that its efforts are guided by the Roadway Departure Strategic Approach and Plan, which involves implementing countermeasures that address roadway departure crashes that fall into three main categories or objectives: 1. Keep vehicles on the roadway, 2. Provide for safe recovery, and 3. Reduce crash severity. The countermeasures that are included within these three categories are highlighted in the following. Objective Strategies Keep vehicles from encroaching into opposite lane Install centerline rumble strips for two-lane roads Install profiled thermoplastic strips for centerline Provide wider cross-sections on two-lane roads Provide center two-way, left-turn lanes for four- and two-lane roads Reallocate total two-lane roadway width (lane and shoulder) to include a narrow buffer median Minimize the likelihood of crashing into an oncoming vehicle Use alternating passing lanes on four-lane sections at key locations Install median barriers for narrow-width medians Table 3. Objectives and strategies for addressing head-on crashes (6).