Roadway Departure Safety: A Manual for Local Rural Road Owners
1. Introduction and Purpose
Why Has This Manual Been Developed?
Local rural roads vary from two-lane paved highways to gravel or dirt roads in mountainous, forest, or tribal areas. A portion of these roadways lack basic signing, pavement markings, and appropriate alignment and delineation features. In many cases local agencies have no plans for improvements due to factors such as funding, low traffic volumes, or topographical challenges.
This document provides local road practitioners with relevant information to reduce roadway departure crashes on the roadway network. It discusses identifying locations with historical or potential rural roadway departure issues and countermeasures that address them. It offers information on the procedures and processes to improve safety by reducing the potential for roadway departure crashes.
Local roads are managed by more than 38,000 counties, villages, towns, and tribal governments.1 Local administrators, township managers, and public works officials maintain and operate a variety of road types; often roadway safety and infrastructure maintenance may be only a small part of their job. The information is geared toward local road managers and other practitioners with responsibility for operating and maintaining local roads, regardless of safety-specific highway training. This document is designed to provide the practitioner with targeted information on roadway departure safety.2 It is not intended as a comprehensive guide for improving roadway departure crashes. It does, however, provide a framework that can be used to assess and improve the safety of the local road network and its potential for this type of crash.
In 2008 the Fatality Analysis Reporting System (FARS) indicated that 56 percent of fatalities on U.S. roadways occurred in rural areas. This is out of proportion, since rural roadways account for just 40 percent of all vehicle miles traveled nationally.3
There were 17,818 fatal roadway departure crashes in the same year, which was 53 percent of the fatal crashes in the United States.4 More than 28 percent of all fatal crashes were associated with horizontal curves. The average crash rate for horizontal curves is about three times that of other types of highway segments. About three-quarters of curve-related fatal crashes involve a single vehicle leaving the roadway and striking trees, utility poles, rocks or other fixed objects, or overturning.5 Eleven percent are head-on crashes, which are the result of a vehicle entering the opposing lane.6 This can occur when a driver enters the opposing lane to maintain speed around the curve, or when a driver overcorrects after running off the right side of the roadway.
To reduce the number and severity of roadway departure crashes, safety practitioners focus on a hierarchy of three objectives:
A data-based approach to identifying roadways with a history of roadway departure crashes and those with the potential for these crashes is discussed in this document. Potential locations are based on factors such as road geometry and the presence of fixed objects in the clear zone.
When working to reduce roadway departure crashes on the local rural road network, the practitioner should consider the implementation approach. Typical approaches include:
For the systematic approach the primary basis is crash types and proven safety countermeasures with specific crash locations selected based on those types.
In one application of the systematic approach, common crash types are selected from analysis. Locations experiencing these crash types and locations with similar geometric features as those experiencing selected crash types are chosen and treated systematically with low cost proven safety countermeasures.
Another application of the systematic approach begins with identifying low-cost, effective countermeasures to common traffic safety issues. Once a basic set of countermeasures is identified, the crash data system is analyzed to choose locations where the countermeasures can be cost-effectively deployed. Estimates of the impacts of implementation can be made in terms of deployment cost and the benefits measured in traffic crash reduction.
Benefits of the systematic approach may include:
Drawbacks of the systematic approach may include:
The spot location approach has typically been based exclusively on an analysis of crash history. Due to the fact that some locations in a jurisdiction will likely have a significantly higher number of crashes than most of the others, it is important to identify those locations and treat them accordingly.
The benefits to the spot location approach may include:
Drawbacks of the spot location approach may include:
The spot location approach to traffic safety can be implemented in parallel with the systematic approach to provide the best combination of safety treatments in a jurisdiction. In addition, the spot location approach could be applied to those locations that have had low cost countermeasures installed systematically but, after an assessment, continue to show a higher than average crash rate.
The comprehensive approach introduces the concept of the "4 E's of Safety": Engineering, Enforcement, Education, and Emergency Medical Services (EMS). This approach recognizes that not all locations can be addressed solely by infrastructure improvements. Incorporating other elements is often required to achieve marked improvement in rural safety.
Some roadway segments will be identified that have frequent driving violations for which targeted enforcement is an appropriate countermeasure. In general, the most common violations are speeding, failure-to-yield, aggressive driving, failure to wear safety belts, and driving while impaired. When locations are identified that have reports and observations of these violations, coordination with the appropriate law enforcement agencies is needed to deploy visible targeted enforcement at the identified segments and corridors to reduce the potential for future driving violations and related crashes. Education and outreach efforts should supplement enforcement to improve the effect of each.
State highway agencies have developed statewide plans to address roadway departure safety problems. As local agencies learn about their own roadway departure safety needs, the State highway agency and State Local Technical Assistance Program (LTAP) office could be of assistance.
Beginning in 2005, States were required by the transportation legislation to develop an SHSP to be eligible for Federal safety funding. An SHSP is a statewide-coordinated safety plan that provides a comprehensive framework for reducing highway fatalities and serious injuries on all public roads. It is developed by the State highway agency in a cooperative process with local, State, Federal, and private sector safety stakeholders. The SHSP is a data-driven, comprehensive plan that establishes statewide goals, objectives, and key emphasis areas and integrates the four E's of safety – engineering, education, enforcement and emergency medical services. In most SHSPs, roadway departure is listed as a key emphasis area.
The purpose of an SHSP is to identify the State's safety needs and guide investment decisions to achieve significant reductions in highway fatalities and serious injuries on all public roads. The SHSP allows all highway safety programs in the State to work together in an effort to align and leverage its resources. It also positions the State and its safety partners to address the State's safety challenges on all public roads collectively.
There are two Federally-funded safety programs related to the SHSP that are potentially available for local public agency use:
For additional information about these safety programs and the SHSP requirements, see Appendix A for links to the Federal Highway Administration (FHWA) websites on each topic.
The Federal Highway Administration currently offers roadway departure technical assistance to State highway agencies in the form of crash data analysis and implementation plan development. Roadway Departure Implementation Plans have been developed for Kentucky, Louisiana, North Carolina, Oregon, South Carolina, and Tennessee, with additional State plans at various stages of development. Each plan is designed to address roadway departure safety issues on both State and local roadways.
In participating States, FHWA has developed a data analysis package focused on crash history and roadway attributes for each state, and a set of strategies that can be used to reduce roadway departure crashes. A set of cost-effective countermeasures, deployment levels, and funding needs is identified to reduce the number and severity of roadway departure crashes in the State by a certain amount. The final plan quantifies the costs and benefits of a roadway departure-focused initiative and provides a step-by-step process for implementation.7
The purpose of this document is to provide information on effectively identifying roadway departure safety issues and countermeasures that address them, leading to the effective implementation of safety projects to improve safety on affected roadways. This includes pertinent information on conducting field reviews, identifying rural roadway segments with multiple crashes and/or high potential for future crashes, and selecting the appropriate low-cost improvement to implement on these roadways.
This document is geared toward local road managers and other practitioners with responsibility for operating and maintaining local roads regardless of training. In many cases, the person responsible for highway safety may have multiple responsibilities including public works functions such as water and wastewater treatment, trash collection, and snow removal. In these cases, roadway safety may be only a small part of the job. The document is intended to provide appropriate, focused roadway departure safety information in one report.
This report suggests a process for the planning and implementation of roadway departure safety improvements. The processes which are discussed in this document can be summarized in Figure 1.
Section 2 provides an overview of the types of data to collect for the identification of problem roadway segments. It describes the types of information available and how they can be used, and it defines and describes various approaches for implementing safety strategies.
Section 3 summarizes the types of analyses that can be conducted to determine if roadway departure countermeasures should be implemented. This discussion builds on the information discussed in Section 2 and provides definitions and examples of the factors that should be considered.
Section 4 provides a description of selected countermeasures that have been shown to improve safety to address roadway departure crashes on local rural roads. They include basic countermeasures such as standard curve warning signing and curve delineation, and also systematic solutions like rumble strips and the safety edge. This section also provides an example of a recommended process to document the information and the decisions made about the countermeasure(s) to be installed.
The process to complete an evaluation of installed treatments is presented in Section 5. After the countermeasures are installed, assessing their effectiveness will provide valuable information and can help determine which countermeasures should continue to be installed on other roadways to make them safer as well.
Section 6 includes case studies of local jurisdictions around the country addressing roadway departure crashes. Examples include signing improvements, enforcement solutions, and road safety audits (RSAs).
Section 7 provides a summary of this manual.
A list of resources and references is presented in Appendix A. This list covers numerous topics from publications that focus on roadway departure countermeasures, research that supports their use, and various studies that document their effectiveness. The Appendix also includes references related to Federal safety funding programs that can potentially be used by local agencies.
Appendix B presents an overview of the Manual on Uniform Traffic Control Devices (MUTCD) minimum requirements for traffic control devices most likely to be used in response to roadway departure crashes. The MUTCD provides the standards used by road managers nationwide to install and maintain traffic control devices on all public streets, highways, bikeways, and private roads open to public travel.
Appendix C contains the formulas to calculate the crash rate of roadway segments. Additionally, examples are included for crash rates by traffic volume and crash rates by length of roadway.
2The Federal Highway Administration (FHWA) defines roadway departure crashes as, "a non-intersection crash which occurs after a vehicle crosses an edge line or a center line, or otherwise leaves the traveled way."
3University of California – Berkeley, Safe Transportation Research and Education Center, "SafeTrec – Rural Road Safety" web page, 2009. Available at http://www.tsc.berkeley.edu/research/ruralroads.html
4Federal Highway Administration, "Roadway Departure Safety" website. Available at: http://safety.fhwa.dot.gov/roadway_dept/horicurves/
5University of California – Berkeley, Safe Transportation Research and Education Center, "SafeTrec – Rural Road Safety" web page, 2009. Available at http://www.tsc.berkeley.edu/research/ruralroads.html
6American Association of State Highway and Transportation Officials, Driving Down Lane Departure Crashes: A National Priority, (Washington, DC: April 2008). Available at: http://downloads.transportation.org/PLD-1.pdf
7For additional information about this initiative, visit the FHWA Strategic Approach to Roadway Departure website at http://safety.fhwa.dot.gov/roadway%5Fdept/strat%5Fapproach/.