Practices for Preventing Roadway Departures (2018)

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1 As reported by the FHWA, from 2013 to 2015, an average of 18,275 fatalities resulted from roadway departure crashes, which is 54% of all traffic fatalities in the United States (1). A roadway departure crash is defined by FHWA as a crash that occurs after a vehicle crosses an edge line or centerline or otherwise leaves the traveled way. Roadway departure crashes result from a variety of contributing factors involving the driver, the vehicle, the highway, and the environment. Preventing these types of crashes, or reducing the injury severity if they do occur, requires a multidisciplinary approach involv- ing engineering, enforcement, education, and emergency medical services. From the high- way perspective, a variety of engineering countermeasures have been implemented by state and local transportation agencies to mitigate roadway departure crashes. For the purposes of this synthesis, an engineering countermeasure is any traffic control device (e.g., sign, signal, pavement marking), geometric design feature (e.g., shoulder, horizontal alignment, clear zone, superelevation), roadside safety hardware (e.g., guardrail, cable median barrier), or other physical change to the roadway implemented to counter a safety problem either at a spot location, a section of road, or, more broadly, within the agency’s road network. Engineering countermeasures have been used on all roadway types (from local two-lane roads to Interstate freeways) and in all area types (rural, suburban, and urban) to achieve the following objectives: • Keep vehicles on the roadway, • Minimize the consequences of leaving the roadway, and • Reduce head-on and cross-median crashes. The objectives of this synthesis project were to identify and summarize countermeasures being used by state departments of transportation (DOTs) to prevent roadway departure crashes and to identify the data-driven advantages and disadvantages of these counter- measures. More specifically, the project was to gather information on: • Relative extent of use of the countermeasures (i.e., rarely, sometimes, often); • Any implementation hurdles that were overcome (e.g., policy, maintenance, public feedback); • Programmatic implementation strategies (e.g., hot spots versus systemic); and • Agency countermeasure evaluations [e.g., before-and-after safety analysis, crash modi- fication factors (CMFs) or system performance functions (SPFs), durability studies, life-cycle cost analysis]. The information gathering portion of the project was conducted in the following steps: • A literature search and review—initially a preliminary literature search to identify the potential list of engineering countermeasures, and then a more complete review of published literature on the safety effects for each of the countermeasures; S U M M A R Y Practices for Preventing Roadway Departures

2 Practices for Preventing Roadway Departures • An online questionnaire sent to all 50 state DOTs and that of Washington, D.C., for the purpose of determining the countermeasures being used by those agencies and related issues; and • Interviews with representatives in three states to develop case examples for specific successful countermeasures and roadway departure programs. The initial literature search identified 20 countermeasures, which in turn were used as the focus of a questionnaire survey of the states’ practices. The state survey also explored: • Safety problem identification and countermeasure implementation programs being followed, • Additional countermeasures being used, • Evaluations of safety effectiveness of countermeasures, • Evaluations of non-safety issues related to materials and maintenance, • Research needs of the states, and • Influence (if any) of emerging vehicle technologies, including autonomous vehicles. Forty-one state DOTs responded to the questionnaire, equating to an 80% response rate. Key findings from the survey are summarized in the following. All of the states are using the traditional high-crash-frequency or crash-rate approach (also known as the hot-spot approach) for identifying problem locations. However, most of the states are also using the systematic and/or systemic approaches. Both are considered espe- cially effective for implementation of low-cost countermeasures, with the former approach applying selected measures to certain crash types, and the latter approach applying applicable countermeasures to sites with high-risk roadway features correlated with severe crash types. Most of the states were using all of the 20 countermeasures to a varying level. Based on the responses from the survey, three additional countermeasures were identified. The counter- measures that 90% or more of the states responded they were using are: • Shoulder rumble strips (100%), • Centerline rumble strips (98%), • Flashing beacon on warning signs (98%), • Tree removal (98%), • Increased sight distance on curves (93%), • Superelevation improvement (93%), • High-friction surface treatment (90%), and • Cable median barriers (90%). The other part of the equation is how frequently the states used a particular counter- measure. To obtain a measure of this factor, the respondents were given three choices: often, sometimes, and rarely. Without any guidance on what amount of application in terms of miles or number of locations should be assigned to each choice, wide variations among the respondents should be expected. With that caveat, the survey revealed that shoulder rumble strips were being used often by 85% of the states. Other countermeasures being used often, at a level greater than 50%, were SafetyEdge (63%), edge-line rumble strips (59%), cable median barriers (57%), and centerline rumble strips (55%). Those countermeasures that have been shown to be especially effective in reducing road- way departure crashes or their severity include: • Shoulder, edge-line, and centerline rumble strips, • SafetyEdge, • High-friction surface treatment, • Cable median barriers,

Summary 3 • Increasing the clear zone, • Flattening side slopes, and • Increasing sight distance for curves. The use of the first four countermeasures has become so widely accepted as effective that some states are now integrating them into their design guidelines with criteria as to where they should be deployed. Agencies were given the opportunity to raise any other issue related to the application of countermeasures for roadway departure crashes. Two issues raised were: • Unsafe driving behaviors such as speeding, distraction, fatigue, and driving under the influence of alcohol or drugs are major contributing factors to roadway departure crashes. Many of the engineering countermeasures being used can target these behaviors, but the use of enforcement and education strategies should be included as part of a comprehen- sive safety program. • It is sometimes difficult to convince local road owners (e.g., towns, small counties) to deploy even low-cost signs and marking countermeasures. A systemic approach that iden- tifies high-risk areas is seen as a method for justifying such countermeasures. An overall push to implement as many of the systemic countermeasures as possible as part of a main- tenance program was considered a long-term solution to bringing down the total number and severity of roadway departure crashes. One of the items in the questionnaire to the states was “indicate which of the counter- measures that your state is using need more research.” The collective responses from the states indicated that further research is needed for nearly all of the countermeasures. While the specific scope of the research was not specified, the states wished to be sure that a certain countermeasure would bring about a reduction in roadway departure crashes and/or a reduction in serious injuries and fatalities. Furthermore, they would like to know if a counter- measure is cost-effective in order to justify the expenditure, especially for the more costly countermeasures. These two basic research needs suggest the need for a comprehensive research program that systematically conducts research on the countermeasures. Ideally, for each countermeasure, the following would be addressed: • The safety effect in terms of changes in crashes and severity, with a goal of developing CMFs that could be posted in the CMF Clearinghouse; • The determination of non-safety impacts, such as public acceptance, life-cycle costs, and maintenance issues, so that the cost-effectiveness of the countermeasures can be determined; and • Guidance for conditions under which the countermeasure is best suited or, on the contrary, should not be used.