Crashes on rural roads often account for a high percentage of all severe crashes, but the density of crashes associated with rural roadways or particular crash types is typically low. A low density of crashes typically does not lead to identifying crash issues or locations of concern within the traditional site-specific analysis process. Instead, this low-density distribution of crashes poses a challenge to addressing safety issues and concerns because a high percentage of severe crashes are not being identified for improvement projects. A further challenge to the low-density issue is that these crashes frequently occur on roadways that are part of the local system that might not have robust data to assist with identifying the locations of concern. This low-density crash situation is often viewed as a rural issue, but similar situations can exist in urban areas, such as crashes involving motorized vehicles and vulnerable road users (e.g., pedestrians, bicyclists, and motorcyclists).
Many traditional network screening techniques for identifying sites for potential safety improvement base investment decisions on the site analysis approach. Such techniques focus primarily on specific locations with a history of severe crashes (often referred to as hot spots or black spots). However, compelling evidence indicates that severe crashes actually are widely distributed across state and local highway systems, and very few individual locations in rural areas and on local systems experience a high number or sustained occurrence of severe crashes. As a result, states will have trouble meeting their safety performance goals by only investing in high-crash locations; some systemic deployment will be needed. Thus, some agencies added a systemic approach to their safety management efforts.
The "Moving Ahead for Progress in the 21st Century Act" (MAP-21) continues the Highway Safety Improvement Program (HSIP) as a core Federal-aid highway program and emphasizes reducing fatal and serious injury crashes on all public roads. The legislation acknowledges that a State’s HSIP should identify projects to improve safety not only on the basis of crash history, but also on crash potential. MAP-21 places a significant emphasis on systemic safety improvements as part of the safety management process. MAP-21 clarifies that systemic safety improvements are eligible highway safety improvement projects. In addition, MAP-21 encourages each state to consider systemic safety improvements as they update their strategic highway safety plan (SHSP).
As part of the HSIP, the requirement to address the potential for crashes to occur suggests the need to include a systemic approach to safety in the safety management process. The systemic approach to safety involves widely implemented improvements based on high-risk roadway features correlated with specific severe crash types. The approach provides a more comprehensive method for safety planning and implementation that supplements and complements traditional site analysis. The approach also helps agencies broaden their traffic safety efforts and consider risk as well as crash history when identifying where to make low-cost safety improvements.
The systemic approach to safety is a data-driven process that involves analytical techniques to identify sites for potential safety improvement and suggests projects for safety investment not typically identified through the traditional site analysis approach. The intent of this complementary approach is to supplement traditional site analysis and provide a more comprehensive and proactive approach to preventing the most severe crashes on our nation’s roadways. Figure 1 illustrates that the systemic and site analysis approaches include the same basic planning elements (problem identification, countermeasure identification, and project prioritization) as reflected in most common safety management processes, including the HSIP. Systemic analysis, however, addresses the crash types that result in a significant number of fatal and serious injury crashes spread across the network rather than focusing only on specific sites experiencing a history of severe crashes (traditional site analysis). The systemic approach to safety does not replace traditional site analysis; high crash locations must still be addressed. Rather, both the site analysis and systemic approaches are necessary to advance a comprehensive safety management program.
Systemic safety planning is the process of evaluating an entire system using a defined set of criteria to identify candidate locations for safety investments to reduce the occurrence of and the potential for severe crashes. The systemic approach to safety is a complementary analytical technique intended to supplement the traditional site analysis approach and results in a more comprehensive safety management program.
The systemic approach to safety:
- Identifies a "problem" based on systemwide data, such as rural lane departure crashes, urban pedestrian crashes, or rural unsignalized intersection crashes. These crashes are often spread across the network with few or no locations experiencing a "cluster" of crashes during a typical 3- to 5-year analysis period.
- Looks for characteristics (e.g., geometry, volume, or location) frequently present in severe crashes. These characteristics, also known as risk factors (For purposes of the Systemic Safety Project Selection Tool, the term "risk factor" refers to a common characteristic of the locations where severe crashes occurred; therefore, the presence of a risk factor at other locations is an indicator of the potential for a future severe crash.), can be used to identify and prioritize locations with few or no crashes that could be potential candidates for safety investments.
- Focuses on deploying one or more low-cost countermeasures to address the underlying circumstances contributing to crashes on a majority of roads. Addressing crash types experiencing low densities (crashes per intersection or mile) but high aggregate numbers steers the decision toward low-cost solutions widely deployed across the system in order to affect a large number of locations.
- Identifies and prioritizes locations across the roadway network for implementation. The prioritization process might take on different forms such as implementing low-cost countermeasures as part of resurfacing, restoration, and rehabilitation (3R) projects or stand-alone safety projects. In either case, the systemic approach to safety represents one of several mechanisms to implement a state SHSP or other local safety plan.
The key to the systemic planning process is the concept of evaluating an entire system using a defined set of criteria that will vary depending on the available data. The result is an inferred prioritization, indicating that some elements of the system are better candidates than others for safety investment. A key question this process sets out to answer is Do all systems and crash types present equal opportunities for crash reduction, or do specific parts of the system and certain crash types offer a greater opportunity for crash reduction?
The Systemic Safety Project Selection Tool (Systemic Tool) builds upon current practices for identifying roadway safety problems and developing highway safety improvement projects. The Systemic Tool fills the current void of analytical techniques and models useful for conducting the systemic approach to roadway safety (current techniques and models focus on site-specific analysis).
Specifically, the Systemic Tool provides the following:
- A step-by-step process for conducting systemic safety planning
- Considerations for determining a reasonable distribution between the implementation of spot safety improvements and systemic safety improvements
- A mechanism for quantifying the benefits of safety improvements implemented through a systemic approach
The Systemic Tool outlines a process that agencies can integrate into existing safety management practices and safety analysis tools. The process guides agencies as they conduct systemic safety planning, determine funding levels for implementation of systemic safety improvement projects, and evaluate the effectiveness of systemic safety programs. The cyclical process illustrated in Figure 2 reflects the three elements of the Systemic Tool as presented in this manual:
- Element 1: The Systemic Safety Planning Process (blue in Figure 2) helps safety analysts identify priority crash types and associated risk factors; evaluate proven, low-cost safety countermeasures; and prioritize alternative candidate locations for systemic safety investment.
- Element 2: A Framework for Balancing Systemic and Traditional Safety Investments (green in Figure 2) provides a framework for setting funding goals between systemic and site analysis programs. Finally,
- Element 3: Evaluation of a Systemic Safety Program (purple in Figure 2) provides high-level direction for evaluating the effectiveness of systemic safety programs.
The Systemic Tool is designed to be flexible and easy to use, resulting in easy-to-understand output. The data requirements for the Systemic Tool are flexible and assist with identifying potential risk factors. The following describes each of these characteristics of the Systemic Tool:
- Flexible–The tool is applicable to a variety of systems, in a variety of locations, and with a variety of crash types.
- Easy to use–The processes are meant to be relatively straight-forward, requiring minimal training and technical assistance.
- Easy-to-understand output–The output is understandable by both program managers and project development engineers who might have no training in traffic safety analysis techniques.
- Flexible data requirements–The data requirements can be matched to what individual agencies can deliver.
- Risk factors–Where possible, the tool helps identify characteristics in addition to crash experience to support the identification of potential risk factors.
This Systemic Tool is organized into five sections and an appendix. This section (Introduction) provides an overview of systemic safety planning and the Systemic Tool. The next three sections are devoted to the three elements of the Systemic Tool, and each of these sections contains examples that illustrate the systemic planning concepts explained in the text. Element 1 describes the four-step systemic safety planning process and concludes with a case study from the Minnesota Department of Transportation (MnDOT). Element 2 provides a framework for determining a reasonable distribution between the implementation of spot safety improvements and systemic safety improvements. Element 3 contains an overview and considerations for evaluating a systemic safety program based on approaches demonstrated to be useful. The final section (References) lists the works cited throughout the document and includes hyperlinks to access reports and websites. The appendix presents several national resources available to practitioners, along with guidance about how the resources can be used to support a systemic safety program.
While using the Systemic Tool, agencies should understand that the process presented needs to be tailored to fit the available data. This might mean that some agencies will have one or two risk factors to consider when prioritizing locations, and others agencies might be able to evaluate numerous characteristics as risk factors. Additionally, the examples and case study simply represent how some agencies have approached a systemic safety analysis process. In the application of the Systemic Tool, it is entirely appropriate for agencies to make changes to adapt to their own data systems.