Factors Contributing to Median Encroachments and Cross-Median Crashes (2014) / Chapter Skim
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Pages 72-84
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72 Introduction This appendix describes methods to reduce the frequency and severity of median-related crashes on divided highways. Guidelines for reducing median-related crashes can be classified into three general approaches: 1.
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73 following discussion reviews each design treatment and documents known effectiveness measures for those treatments. Several of these treatments, by their nature, have high costs and may be most appropriate for consideration in new construction and reconstruction projects, rather than for application to existing roadways.
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74 New HSM procedures for freeways developed in NCHRP Project 17-45 (Bonneson et al., 2012) include the following crash modification functions (CMFs)
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75 (AASHTO, 2011a) recommends the use of 1V:6H slopes in design of medians.
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76 Provide Wider Median Shoulder The median or inside shoulder of a divided highway is intended as a primary recovery area for vehicles that begin to leave the roadway and, in some cases, as a primary stopping and recovery area. This distinction is made because many highway agencies prefer to provide relatively narrow (4-foot)
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77 Increase Separation Between On- and Off-Ramps Research by Harwood et al.
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78 c = regression coefficient (0.001 for all crashes) d = regression coefficient (0.198 for FI crashes and 0.0 for PDO crashes)
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79 • Improve delineation; • Provide transverse pavement markings; • 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; and • Raise the state of preparedness for winter maintenance.
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80 more visible. No formal effectiveness measures for this treatment are available.
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81 speed comes from the streaming of information or "optical flow" in peripheral vision. After driving long distances, drivers become "speed-adapted" and have difficulty in reducing speed, even when they are aware of the adaptation and try to counter it.
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82 were difficult to detect. In both cases speed variance decreased; however, headway was not affected (Rämä, 1999)
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83 Mason, J M., et al., Median Safety Study (Interstates and Expressways)
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Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005)
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