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4 Background 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 for those years (1). A roadway departure crash is defined by the FHWA as a crash that occurs after a vehicle crosses an edge line or centerline or otherwise leaves the traveled way (1). Roadway departure crashes result from one or more of a variety of contributing factors involving the driver, the vehicle, the highway, and the environment. Prevention of these types of crashes, and reducing the injury severity if they do occur, requires a multidisciplinary approach involving engineering, enforcement, education, and emergency medical services. From the highway perspective, a variety of engineering countermeasures have been imple- mented by state and local transportation agencies to mitigate roadway departure crashes. 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. Before proceeding, the term âcountermeasureâ needs to be defined. In the highway safety literature, the terms âobjectives,â âstrategies,â âtreatments,â and âcountermeasuresâ are used separately and at times interchangeably. In the Highway Safety Manual (HSM), the term âcounter- measureâ is used throughout Chapter 3. While not formally defined in the HSM, the following statements are made: CMFs [crash modification factors] are generally presented for the implementation of a particular treatment, also known as a countermeasure intervention, action, or alternative design. Examples include illuminating an unlighted road segment, paving gravel shoulders . . . (2) The Crash Modification Factors (CMF) Clearinghouse defines a countermeasure as: For road safety engineers . . . typically a physical change to the infrastructure of a road section or intersection, such as the addition of signs, signals, or markings, or a change in roadway design. (3) For the purpose of this synthesis, an engineering countermeasure is any traffic control device (e.g., sign, signal, pavement marking), geometric design feature (e.g., shoulder, hori- zontal 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, section of road, or, more broadly, within an agencyâs road network. C H A P T E R 1 Introduction
Introduction 5 Synthesis Objective The highway safety literature is robust concerning the development and evaluation of these countermeasures, but what has not been surveyed and documented is the state of the practice among the state departments of transportation (DOTs) for their use or non-use. Therefore, the stated objectives of this synthesis project were to identify engineering countermeasures being used by state DOTs to prevent roadway departure crashes and also to identify their data- driven advantages and disadvantages. The synthesis was to focus on enhancements, treat- ments, and improvements of existing roads. The information to be gathered was to include: â¢ Countermeasures organized by the three objectives mentioned previously; â¢ Relative extent of use (i.e., rarely, sometimes, often); â¢ Conventional and innovative countermeasures; â¢ 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, CMFs or system performance functions (SPFs), durability studies, life-cycle cost analysis]. Approach 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 poten- tial list of engineering countermeasures, and then a more complete review of published literature for each of the countermeasures that focused on their safety effectiveness. â¢ An online questionnaire sent to all 50 state DOTs and that of Washington, D.C., for the pri- mary purpose of identifying the countermeasures being used by those agencies and their expe- riences with them. There were 41 agencies that responded, equating to an 80% response rate. â¢ Follow-up interviews with representatives of three states, which served as case examples for roadway departure safety programs and for specific countermeasuresâ successes. Report Contents The contents of the remaining chapters are as follows: â¢ Chapter 2 documents the identification of the initial list of countermeasures that served as the focus for the state DOT survey of practices. â¢ Chapter 3 presents the results of the survey questionnaire. A large portion of this chapter is devoted to the statesâ practices for each of the identified countermeasures. â¢ Chapter 4 documents the key findings, conclusions, and suggestions for future research. The appendices (which are available at www.TRB.org by searching for âNCHRP Synthesis 515â) include the following: â¢ Appendix A presents the questionnaire sent to each state but condensed to reduce the page length. â¢ Appendix B contains 33 tables that show the responses from the states for each of the questions. â¢ Appendix C is the Massachusetts Lane Departure Crash Data Analysis, which illustrates how one state identifies roadway departure crashes. â¢ Appendix D is a case study document that describes how Arizona used the performance-based practical design approach to evaluate two safety roadside departure crash countermeasuresâ widening shoulders and improving superelevation. â¢ Appendix E is a project case study on high-friction surface treatments from Kentucky. â¢ Appendix F provides information about noteworthy programs being conducted by three statesâAlabama, Georgia, and North Carolinaâfor the implementation of countermeasures.