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63 S E C T I O N 6 Guidelines for reducing median-related crashes can be classified into three general approaches: ⢠Design guidance to reduce consequences of median encroach ments, ⢠Design guidance to reduce likelihood of median encroach- ments, and ⢠Countermeasures to reduce likelihood of median encroach- ments. Highway agency efforts to improve median safety on divided highways have focused primarily on the first approach pre- sented aboveâdesigning or retrofitting medians of divided highways to reduce the consequences of median encroach- ments. The AASHTO Roadside Design Guide (55) and other resources provide guidance on implementing this approach. While this research encourages the first approach, it also directs highway agency attention to the second and third approaches, which are intended to reduce the likelihood that motorists will run off the road into the median in the first place. An effective program to reduce median-related crashes should consider a mix of these three approaches. Table 6-1 summarizes the design guidance and counter- measures that should be considered in median safety programs. The table includes both general objectives for implementing each of the three approaches to reducing median-related crashes identified above and specific design guidance or counter- measures that should be considered for implementation. Appendix D presents detailed guidelines for reducing median-related crashes. The guidelines address the three overall approaches for reducing median-related crashes, the objectives of highway agency actions, and the specifics of design guidelines and countermeasures for implementation. The discussion of each guideline or countermeasure describes the guideline or countermeasure and presents what is known about its effectiveness. The appendix is in a form that could be used as a stand-alone guide. Guidelines for Geometric Design and Countermeasure Implementation to Reduce Median-Related Crashes
64 Objective Design guidance/countermeasure Design guidance to reduce consequences of median encroachments Minimize potential for collision with fixed objects Relocate or remove fixed objects in median Reduce consequences of collision with fixed objects Provide barrier to shield objects in median Reduce likelihood of cross-median collisions Provide wider medians Provide continuous median barrier Reduce likelihood of vehicle overturning Flatten median slopes Provide U-shaped (rather than V-shaped) median cross section Provide barrier to shield steep slopes Design guidance to reduce likelihood of median encroachments Improve design of geometric elements Provide wider median shoulder Minimize sharp curves with radii less than 3,000 feet Minimize steep grades of 4 percent or more Improve design of mainline ramp terminals Increase separation between on- and off-ramps Minimize left-hand exits Improve design of merge and diverge areas by lengthening speed-change lanes Simplify design of weaving areas Increase decision sight-distance to on-ramps Countermeasures to reduce likelihood of median encroachments Reduce driver inattention Provide edgeline or shoulder rumble strips Decrease side friction demand Improve/restore superelevation at horizontal curves Increase pavement friction Provide high-friction pavement surfaces Improve drainage Improve road surface or cross-slope for better drainage Reduce high driver workload Improve visibility and provide better advance warning for on- ramps Improve visibility and provide better advance warning for curves and grades Improve delineation Encourage drivers to reduce speeds Provide transverse pavement markings Minimize weather-related crashes Provide weather-activated speed signs Provide static signs warning of weather conditions (e.g., bridge freezes before road surface) Apply sand or other materials to improve road surface friction Apply chemical de-icing or anti-icing as a location-specific treatment Improve winter maintenance response times Install snow fences Raise the state of preparedness for winter maintenance Table 6-1. Design guidelines and crash countermeasures to reduce median-related crashes.
