Guidelines for Treatments to Mitigate Opposite Direction Crashes (2022)

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30 Reducing Severity of Crash This chapter covers the cable median barrier countermeasure that may prevent opposite direction crashes as well as a broader range of crash types. Table 16 summarizes this cable median barrier countermeasure. This treatment focuses on restricting the vehicle’s path so that a vehicle can have an opportunity to safely redirect and enter the road or impact a more forgiving object in exchange for the more hazardous crash. The cost of this type of treatment also varies more than those in Chapter 3 and Chapter 4, as some locations will require very minor adjustments while others often require the purchase of additional ROW or the construction of additional infrastructure. There may also be significant added expense associated with ongoing maintenance activities such as that required for the cable median barrier. C H A P T E R 5 Countermeasure Project Cost Crash Type Facility Type Install cable median barrier* Moderate Head-on and opposite direction sideswipe (in median) Divided highway * Though other barriers such as rigid concrete barrier or guardrail may be considered, the cable median barrier is a unique treatment specifically targeted toward opposite direction crashes in or adjacent to a roadway median. Table 16. Countermeasure to reduce severity of crash. Install Cable Median Barrier Treatment/Countermeasure: Install Cable Median Barrier Project Type/Cost: Crash Type: Median crashes (head-on or opposite direction sideswipe) Facility Type/Characteristics: Divided highway Low Moderate High WHAT (Introduction) A cable median barrier is a longitudinal barrier used to contain or redirect errant vehicles that leave the roadway by keeping them from encountering terrain features and roadside objects or permitting vehicles to enter opposing travel lanes (Figure 14). The most typical cable median barrier is a three-strand steel cable barrier system connected to a series of posts (34).

Reducing Severity of Crash 31   WHY (Safety State of the Practice) Cable barrier absorbs more of the energy in the crash than semi-rigid or rigid barrier, and therefore is more likely to result in a less severe crash. Several studies have documented cable median barriers applied at multiple locations with an emphasis on their potential to reduce cross-median crashes. Table 17 summarizes key findings from related studies. General Observations Based on previous studies, users can expect to see a reduction in cross-median crashes as well as opposing direction crashes of approximately 91 to 96 percent for principal arterial interstates in rural regions. Reductions of 62 to 65 percent can be expected for interstate and freeway cross-median crashes. Iowa noted a 62 percent reduction in fatal crashes while Utah observed a 44 percent reduction in fatal plus incapacitating injury crashes. It should be noted that PDO crashes may increase following an installation of cable median barriers, because vehicles that previously could have recovered in the median undamaged now strike the cable barrier, resulting in damage to the vehicle and the cable barrier. This potential increase in PDO crashes is often more than offset by the reduction in severe crashes. WHERE (Application Issues) Design The designer should consider the width and slope of the median when installing cable median barriers. Missouri Department of Transportation’s (DOT’s) Engineering Policy Guide for their cable median barrier program (39) recommends that for medians at least 30 ft wide, the cable barrier should be installed 4 ft down-slope of the edge of the shoulder. For medians narrower than 30 ft, the cable barrier should be installed per the graphs in NCHRP Report 711 (40). Care should also be taken when installing cable barrier at horizontal or vertical curve locations, and (Photograph provided by Texas A&M Transportation Institute) Figure 14. Cable median barrier.

32 Guidelines for Treatments to Mitigate Opposite Direction Crashes cable barriers should be installed as far away from the traveled way as possible while maintaining the proper orientation and performance of the system. Missouri DOT (39) also recommends that new cable median barrier be installed on a corridor- wide basis. A corridor should have similar geometry, traffic volumes, and crash histories. The placement of cable median barrier on this corridor should also be configured with a logical termini location. Intermittent, short length cable median barrier should be used sparingly. Operations A potential concern commonly noted in the literature is whether cable median barriers pose additional risk to motorcyclists, though research has generally shown that cable barriers are not much different from other types of barriers in their effects on motorcyclists who strike them. Both the Missouri DOT and the Cooner et al. (41) guidelines provide recommendations for accommodation of emergency responders. Cooner et al. recommend that the maximum dis- tance between breaks in the cable barrier system that allow emergency vehicle access should be 3 miles, and emergency response agencies should have educational materials to provide them with clear and concise guidance on when and how to safely cut the cable when a vehicle is entangled after an impact. Missouri DOT (39) indicates that emergency crossovers for free- ways should be spaced approximately 2.5 miles apart; additional crossovers near sparsely spaced interchanges may be required to facilitate snow removal. Study Location(s) Year Median Width (ft) Area Type Percent Reduction in Crashes (%) Source CM+ Cross-Median Crashes (KABCO) (KABCO) (K) (KA) Principal Arterial Interstate IN 2009 30-50 Rural 91 NR NR NR (35) IN 2009 >50 Rural 96 NR NR NR (35) UT 2011 NR All NR 62 NR 44 (36) IA 2018 NR NR NR NR 62 NR (37) Principal Arterial Other Freeways and Expressways WA 2013 NR NR NR 65 NR NR (38) NR – not reported CM+ refers to cross-median crashes plus frontal and opposing direction sideswipe and head-on Note: The selection process included studies with three-star ratings or more at the CMF Clearinghouse. Table 17. Summary of cable median barrier studies.