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FOREWORD Highway administrators, engineers, and researchers often face problems for which information already exists, either in documented form or as undocumented experience and practice. This infor- mation may be fragmented, scattered, and unevaluated. As a consequence, full knowledge of what has been learned about a problem may not be brought to bear on its solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recommended practices for solving or alleviating the problem. There is information on nearly every subject of concern to highway administrators and engineers. Much of it derives from research or from the work of practitioners faced with problems in their day- to-day work. To provide a systematic means for assembling and evalu ating such useful information and to make it available to the entire highway community, the American Association of State High- way and Transportation Officialsâthrough the mechanism of the National Cooperative Highway Research Programâauthorized the Transportation Research Board to undertake a continuing study. This study, NCHRP Project 20-05, âSynthesis of Information Related to Highway Problems,â searches out and synthesizes useful knowledge from all available sources and prepares concise, documented reports on specific topics. Reports from this endeavor constitute an NCHRP report series, Synthesis of Highway Practice. This synthesis series reports on current knowledge and practice, in a compact format, without the detailed directions usually found in handbooks or design manuals. Each report in the series provides a compendium of the best knowledge available on those measures found to be the most successful in resolving specific problems. PREFACE By Jo Allen Gause Staff Officer Transportation Research Board More than half of all traffic fatalities result from roadway departure crashes. This type of crash occurs after a vehicle crosses an edge line or centerline or otherwise leaves the traveled way. A variety of engineering strategies, often referred to as countermeasures, have been implemented by state and local agencies to prevent roadway departure crashes and reduce the severity of injuries if crashes do occur. This synthesis documents countermeasures being used by state departments of transportation to prevent roadway departure crashes. Information for this study was gathered through a literature review and a survey of state depart- ments of transportation. Three case examples provide examples of specific countermeasures and roadway departure programs. Appendices A through F can be found at www.TRB.org by searching for âNCHRP Synthesis 515.â Hugh W. McGee, Sr., collected and synthesized the information and wrote the report. The mem- bers of the topic panel are acknowledged on page iv. This synthesis is an immediately useful docu- ment that records the practices that were acceptable with the limitations of the knowledge available at the time of its preparation. As progress in research and practice continues, new knowledge will be added to that now at hand.
Note: Photographs, figures, and tables in this report may have been converted from color to grayscale for printing. The electronic version of the report (posted on the web at www.trb.org) retains the color versions. 1 Summary 4 Chapter 1 Introduction 6 Chapter 2 Engineering Countermeasures for Roadway Departure Crashes 12 Chapter 3 Survey of the State of the Practice 43 Chapter 4 Conclusions 48 References 50 Appendices C O N T E N T S
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 agencyâs 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: â¢ Keep vehicles on the roadway, â¢ Minimize the consequences of leaving the roadway, and â¢ 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: â¢ Relative extent of use of the countermeasures (i.e., rarely, sometimes, often); â¢ Any implementation hurdles that were overcome (e.g., policy, maintenance, public feedback); â¢ Programmatic implementation strategies (e.g., hot spots versus systemic); and â¢ 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: â¢ A literature search and reviewâinitially 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 â¢ 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 â¢ 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 statesâ practices. The state survey also explored: â¢ Safety problem identification and countermeasure implementation programs being followed, â¢ Additional countermeasures being used, â¢ Evaluations of safety effectiveness of countermeasures, â¢ Evaluations of non-safety issues related to materials and maintenance, â¢ Research needs of the states, and â¢ 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: â¢ Shoulder rumble strips (100%), â¢ Centerline rumble strips (98%), â¢ Flashing beacon on warning signs (98%), â¢ Tree removal (98%), â¢ Increased sight distance on curves (93%), â¢ Superelevation improvement (93%), â¢ High-friction surface treatment (90%), and â¢ 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: â¢ Shoulder, edge-line, and centerline rumble strips, â¢ SafetyEdge, â¢ High-friction surface treatment, â¢ Cable median barriers,
Summary 3 â¢ Increasing the clear zone, â¢ Flattening side slopes, and â¢ 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: â¢ 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. â¢ 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 âindicate which of the counter- measures that your state is using need more research.â 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: â¢ 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; â¢ 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 â¢ Guidance for conditions under which the countermeasure is best suited or, on the contrary, should not be used.