Agencies interested in adding a systemic component to their highway safety program quickly realize their next decision involves determining how to distribute their safety investments among projects identified through the traditional site analysis approach and projects identified through the systemic approach. Element 2 of the Systemic Safety Project Selection Tool provides a framework determining an appropriate balance of safety investments between the site analysis and systemic approaches. The framework supports a program manager’s decisions about the general distribution of the safety investments given particular crash and roadway system characteristics. A framework is more appropriate than a prescriptive process because each agency has unique considerations.
The decision support framework begins with a review of historical safety investments and crash history to gain an understanding of past agency decisions. Looking back is often instructive when considering a new path to move forward. The path forward is then based on a combination of understanding the effectiveness of historical safety investments, understanding how an agency’s goals, priorities, and crash and roadway characteristics lend themselves to a systemic approach, and assessing the potential benefit to be gained with systemic investment.
Consideration of an agency’s goals, priorities, and crash and roadway characteristics provides a safety program manager with useful clues for making decisions about adding a systemic component to their safety program and allocating funding in support of identified projects. Following are some examples of these considerations:
- Adopting a goal to reduce severe crashes suggests a need to include a systemic component to safety management efforts because severe crashes tend to be scattered across a roadway system, making it difficult to isolate high-crash locations.
- Adopting cross-median head-on crashes as a priority suggests a need to include a systemic component because these types of crashes rarely occur at the same location, but supporting data may show that these crashes occur in similar locations (e.g., overrepresented in the vicinity of interchanges).
- Adopting deployment of center-line rumble strips as a priority safety countermeasure suggests the need to include a systemic component because it is rare for multiple severe head-on crashes to occur at the same location.
- Adopting a goal to address safety on the rural secondary system as a priority suggests the need to include a systemic component because, although these road systems often account for a high percentage of severe crashes, they typically have very low crash densities.
Thus, the decision to invest funding in systemic improvements is influenced by program goals rather than justified solely through analysis of the benefits to be gained from implementation and maintenance costs expended.
Reviewing past funding practices helps answer the following questions about an agency’s historical investment in safety improvement projects:
- Which countermeasures were implemented?
- Where were countermeasures implemented (i.e., what roadway systems)?
- Which crash types were these countermeasures addressing?
- Were these crash types and countermeasures identified as a priority in the SHSP?
- What was the outcome (i.e., countermeasure influence on focus crashes)?
Answers to these questions provide insight for safety program managers. If the review determines that the historical safety investments were consistent with SHSP priorities, the investments effectively reduced focus crashes, the results of the historical investments were satisfactory, and the same crash types and roadway facilities are expected to be a priority going forward, only a small portion of an agency’s safety investments would likely need to be diverted to supporting projects identified through a new systemic approach. However, if the review determines that these criteria were not achieved, then safety program managers might conclude that it may be necessary to redirect safety investments. This new direction might include allocating safety funds to a systemic safety program aimed at proactively deploying low-cost countermeasures systemwide.
Table 2 illustrates an example of one agency’s efforts to review their historical highway safety investments. This state’s HSIP records were searched, and the investments were disaggregated by project type within three basic categories: Intersection Improvements, Lane Departure Improvements, and Other Improvements. The safety program managers concluded that the Intersection Improvements and Lane Departure Improvements categories were consistent with their SHSP priorities, but several of the specific project types were not. Specifically, the proportion of funding for all safety improvement projects related to traffic signal installation and revisions substantially exceeded the proportion of severe crashes occurring at signalized intersections. In addition, the program managers concluded that within the Lane Departure Improvements category, they had underinvested in road edge enhancements and overinvested in median barriers. This determination was based on crash characteristics that indicated more than seven times as many road departure crashes on two-lane rural roads than cross-median crashes on divided roadways. It is important to understand that the funding distribution was a byproduct of the site analysis approach used to focus on locations with multiple severe crashes. This approach resulted in costly investments at relatively few locations that addressed a small percentage of the total severe crashes. Finally, the safety program managers noted that all of these safety investments were directed toward projects deployed along the state’s highway system, but over 40 percent of their severe crashes occurred on the local system. Based on this review, the safety program managers intend to modify their HSIP investments; going forward, a greater portion of their HSIP funds will be directed toward proactive, low-cost road edge improvement projects developed using the systemic safety planning process and located along two-lane roads on both the state and local highway systems.
A funding determination framework assumes two key points. First, there is no suggestion or expectation that any roadway agency’s safety program will be 100 percent oriented toward deployment of systemic projects. This framework suggests, however, that in every agency there will be some balance between projects derived from the site analysis approach and projects derived from the systemic approach. The systemic safety planning process to identify candidates for safety investment complements an agency’s site analysis approach rather than replaces it. Secondly, there is no suggestion or expectation that one particular portion of the safety investments would apply uniformly across an agency’s entire safety program. The balance between projects implemented through each approach is likely different in different regions of a state (e.g., urban versus rural), on different components of the roadway system (e.g., state versus local), and for different focus crash types (e.g., rear end versus road departure crashes).
Agencies should consider a variety of crash and roadway characteristics to determine the balance of safety investments between site analysis and systemic projects. Such considerations suggest a general balance along a safety funding continuum, with one end representing all site analysis projects and the other end representing all systemic projects. Agencies can develop a continuum with characteristics appropriate for their system. Figure 8 illustrates a continuum using the following recommended characteristics for the funding determination framework:
- Are there many or few high-crash locations in a system? Many high-crash locations suggest directing more HSIP funds toward site analysis projects; few high-crash locations suggest directing more HSIP funds toward systemic projects.
- Is an agency’s safety performance measure total crashes or severe crashes? A performance measure based on total crashes suggests a site analysis safety program; a performance measure based on severe crashes suggests a more systemic safety program.
- Are crashes (or specific focus crash types) overrepresented in urban or rural areas? An overrepresentation of crashes in urban areas suggests a site analysis safety program; an overrepresentation of rural crashes suggests a more systemic safety program might be appropriate.
- What are the identified focus crash types? A safety program focused on all crash types suggests a site analysis program; a focus on specific crash types suggests a more systemic program.
- What are the identified priority locations? A focus on signalized intersections suggests a site analysis program; a focus on unsignalized intersections and horizontal curves suggests a more systemic focus.
Example 10 illustrates the application of this funding determination framework by Minnesota DOT, which is now directing a considerable portion of their safety investments to systemic projects. In the two years since adopting this plan, MnDOT has found that their safety investments are consistent with their safety investment goals, and spending on systemic projects is actually slightly above the minimum goals set for both rural and urban areas.
MnDOT applied the Funding Determination Framework to assess their decisions related to balancing safety investments between site analysis and systemic projects.
- The MnDOT safety program managers shared information they used to support their funds distribution decisions. The following key facts about MnDOT’s organization, priorities, and roadway and crash characteristics are relevant to their funding determination process:
- MnDOT is decentralized, with seven districts in rural areas of the state and one in a major metropolitan area.
- Minnesota has almost 140,000 total miles of roadways; the state system consists of approximately 12,000 miles, and the local secondary system consists of 45,000 miles (which is administered by counties and is virtually all rural).
- MnDOT’s adopted safety performance measure is severe crashes, which are almost equally distributed between the state and local secondary system.
- Almost 70 percent of fatal crashes and 60 percent of serious injury crashes occur outside of Minnesota’s one major metropolitan area.
- Focus crash types include road departure and angle crashes at unsignalized intersections in rural areas, and angle and pedestrian crashes at signalized intersections in urban areas.
- An additional priority location was determined to be horizontal curves along rural two-lane roadways. Almost 30 percent of all severe road departure crashes on MnDOT’s system are in horizontal curves, and more than 50 percent of the severe road departure crashes on the local secondary system are in horizontal curves (by mileage, curves make up less than 10 percent of each of these systems).
To determine a division of their safety investments, MnDOT reviewed historical funding practices and determined that, although severe crashes were almost equally distributed between state and local systems, more than 90 percent of safety investments were directed toward projects on the state system. MnDOT also determined that they did not select projects consistently with priorities indicated by their crash data. Rather, a disproportionate amount of funding had been directed to projects in Minnesota’s major urban area, and a disproportionate amount of that funded the traffic signal installation and revision projects. As a result of this review and a commitment in their SHSP to address severe crashes on all roads in the state, MnDOT adopted an entirely new approach to distributing their HSIP funds. The following framework shows the crash and roadway characteristics the safety program managers considered.
Using this information, MnDOT’s safety program managers decided their overall safety investments needed to be more systemic than site-specific. To accomplish this, the safety program managers:
- Redistributed their safety funds by district based on the distribution of severe crashes. This resulted in directing 70 percent of their safety funds to the seven districts outside of the metropolitan area, which is the opposite of their historical practice.
- Divided the safety funds within each district between the state and the local secondary systems based on the distribution of severe crashes. Statewide, this approach resulted in more than 50 percent of the safety investments being directed toward projects on the local secondary system.
- Analyzed crash characteristics resulting in two conclusions: 1) there were no high crash locations on the local secondary system, and 2) crash densities on the local secondary system were a fraction of those on the state system. The analysis also showed that more than 80 percent of severe crashes were on rural roads; focus crash types were road departure (especially in curves) and angle crashes at through/STOP intersections.
- Directed 100 percent of the safety funds dedicated to local roads to low-cost proactive projects with a focus on dealing with rural road edges, enhanced curve delineation, and STOP-controlled intersections, as a result of the analysis of the crash characteristics.
- Noted that virtually no high crash locations were in their rural districts, and set a goal to direct at least 70 percent of their safety investment to systemic projects on the state system. In the urban district, where some high crash locations did exist, they set a goal to direct at least 30 percent of their safety investment toward systemic projects.
Characteristics Considered by MnDOT for Balancing the Distribution of Safety Investments
Safety program managers can perform a programmatic evaluation of their systemic safety planning process to help determine how much funding to invest in systemic improvements. One purpose for the programmatic evaluation is to gain an understanding of the expected crash reduction based on different levels of investment in the systemic countermeasures. To assist with gaining this understanding, several states have developed spreadsheet tools (similar to the one shown in Figure 9) that estimate the potential crash reduction expected for a systemic program.
These spreadsheet tools use the number of severe crashes or fatalities and serious injuries that occurred across the focus facility type and the size of focus facility type (i.e., number of intersections, curves or miles of roads) to estimate the average annual crash densities. With the typical construction cost and applicable crash reduction/modification factor, a spreadsheet tool can quickly estimate the crash reduction and construction cost when testing different levels of deployment (the input by the safety program manager). Including service life, interest rate, maintenance costs, and traffic growth rates in the tool provides the ability to calculate the benefit-cost ratio for the life of the countermeasure. The output, an estimate of the severe crashes or fatalities and serious injuries that could be prevented across the roadway system, provides safety program managers with information about the value of the systemic investment. Another benefit of this approach to programmatic evaluation is that similar calculations can be completed with the same spreadsheet tool for driver behavior countermeasures, providing documentation about the expected crash or injury reduction for a comprehensive safety management program.
Element 2 of the Systemic Safety Project Selection Tool presents a general framework for balancing site analysis and systemic safety investments. The following three components make up the recommended framework for developing a safety investment plan for systemic and site analysis programs:
- Review past funding practices to provide insight into historical safety spending patterns.
- Apply the funding determination framework to determine the appropriate balance of safety investments.
- Assess the potential benefit to be gained by investing funding in systemic improvements.
Using this data-driven framework, safety program managers can determine general goals for the distribution of safety investments based on crash and roadway characteristics. The framework provides agencies the flexibility to craft funding plans that are consistent with their established goals, priorities, and culture.
There is no precise answer for any agency regarding the distribution of safety investments between candidate projects developed using either a site analysis or systemic approach. Safety program managers are encouraged to decide how to distribute safety investments, move forward, and then review following implementation to determine whether the results are consistent with expectations. If the results indicate a positive effect because of a downward trend in focus crashes, then moving forward would involve continuing along the same safety investment track. If the results were not in line with expectations, then the agency would need to reassess the distribution of the safety investments the following year. The review process continues on an annual basis.