U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
This magazine is an archived publication and may contain dated technical, contact, and link information.
|Publication Number: FHWA-HRT-13-004 Date: May/June 2013|
Publication Number: FHWA-HRT-13-004
Issue No: Vol. 76 No. 6
Date: May/June 2013
Applying a systemic approach can help States get the biggest bang for their buck in reducing crashes.
|During construction of this rural two-lane road, the North Dakota Department of Transportation installed centerline rumble strips, a typical systemic safety improvement.|
The traditional approach to planning safety improvements on roads involves identifying locations with a higher than expected number of crashes and then making needed upgrades at those locations. Over the years, this "site analysis” approach yielded a reduction in the number of locations across the country where multiple fatal crashes have occurred. In fact, the annual number of highway fatalities has dropped from nearly 42,000 in 1994 to less than 33,000 in 2010. At least part of this reduction is the result of the emphasis on safety made at the Federal, State, and local levels.
Mounting evidence indicates that fatal and other life-threatening crashes often are distributed widely across State and local highway systems, in both urban and rural environments, with few individual locations experiencing a high number or sustained occurrence of severe crashes. Consequently, some departments of transportation (DOTs) have adopted a new approach to planning safety improvements on their networks, initiating policies and programs to advance the implementation of low-cost safety countermeasures widely across a roadway network. The widespread implementation of low-cost countermeasures -- that is, deployed everywhere -- is known as a "systematic” approach. In an ideal world, where staff resources and budgets were sufficiently available, the systematic approach might be the preferred solution.
However, at a time when DOTs cannot afford to apply treatments equally at all locations, planners are looking instead to set priorities among potential locations for safety improvements. In this case, planners are adopting a "systemic” approach to implementation. Systemic implementation involves the identification of the locations across the network that have the greatest risk for severe crashes, and then prioritizing those for investments in safety improvements.
The systemic approach involves use of analytical techniques to identify sites for potential safety improvements based on the presence of high-risk roadway features. Examples of possible roadway features that influence crash risk include the number of lanes, median width, and average annual daily traffic. This approach suggests projects for safety investment that typically might not be identified through traditional site analyses with the priority focus on locations where a high number of severe crashes has occurred. The systemic approach complements traditional site analyses and provides a comprehensive and proactive approach to planning safety improvements to help prevent the most severe crashes on the Nation’s roadways, which are typically distributed widely across the network. The systemic and site analysis approaches feature the same basic planning steps included in the Highway Safety Improvement Program (HSIP) and most common safety management processes.
The Moving Ahead for Progress in the 21st Century Act (MAP-21) 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 crash potential. Further, MAP-21 encourages States to consider systemic safety improvements as they update their strategic highway safety plans.
"The systemic approach is well suited to address fatalities that are widely distributed on the highway system, such as the Nation’s rural and local systems, which are parts of our national system that have a large percentage of fatalities and serious injuries,” says Associate Administrator Tony Furst of the Federal Highway Administration’s (FHWA) Office of Safety." It presents an excellent platform to engage our local partners in a ‘toward zero deaths’ vision.”
Most of the existing safety management resources focus on the traditional site analysis approach and methodologies that support data analysis to identify high-crash locations. Recognizing the need to address the lack of analytical techniques and models that emphasize the systemic approach, FHWA developed the Systemic Safety Project Selection Tool. What follows is an overview of the systemic approach and how States can use it to prioritize safety improvements.
The Systemic Safety Project Selection Tool is a cyclical process outlining a series of steps that build on the priorities established in State strategic highway safety plans. The process helps identify the characteristics of locations with severe crashes to support application of safety improvements throughout a roadway system.
The tool builds upon current practices and consists of three elements:
FHWA designed the selection tool to be flexible and applicable to a variety of systems, locations, and crash types. The process is meant to be easy to use and straightforward, requiring minimal training and technical assistance. FHWA designed the tool’s outputs to be understandable to both program managers and project development engineers who may or may not have been trained in techniques for traffic safety analysis. Further, FHWA designed the tool to be adaptable, so individual agencies can modify the tool’s data requirements depending on the availability of local data.
One key to systemic safety planning is evaluating an entire system using a defined set of criteria, which will vary depending on the types of data available. The result is an inferred prioritization, indicating that some elements of the system (those sites with more risk factors present) are more promising than other candidates for safety investments. One key question this process sets out to answer is this: Do all systems and crash types present equal opportunities for crash reductions, or do specific parts of the system and certain crash types offer greater opportunities for reductions? The process of systemic safety planning involves four steps that will answer these questions and result in identifying and prioritizing safety improvement projects.
The systemic safety approach involves identifying a problem, selecting a countermeasure, and prioritizing improvement projects. It starts with different criteria to identify sites with the greatest potential for safety improvement that might lead to a different set of projects. This approach involves looking at systemwide data to analyze and identify systemic safety problems -- basically, large numbers of specific crash types that are scattered across a system with very low crash densities. The approach involves performing microlevel analysis to conduct a risk assessment of network locations. This analysis uses crash data along with site characteristics and traffic data to identify sites with a greater risk for crashes. This process leads to the selection of relevant mitigating strategies that are most appropriate for broad implementation across those locations. The following four steps are involved in this process.
Step 1. The first step is to conduct a systemwide analysis of crash data to identify the sites whose target crash types are associated with the greatest number of injury and fatal crashes, which may also be the sites with the greatest potential for safety improvement.
After selecting the target crash types, the next task is to answer the question: What are the characteristics of the locations where the target crashes are occurring? One useful approach and tool for this analysis is creation of a "crash tree” diagram, which can take a number of different formats, depending on the capabilities of the DOT’s system for storing crash records. A typical crash tree might include information such as the jurisdiction (State or local), general location (rural or urban), roadway type (freeway, expressway, or conventional two-lane road), segment or intersection, and type of intersection control. The crash tree helps engineers identify and select the facility types and roadway and traffic control characteristics of the locations where the target crash types occur most frequently.
The final task in this step is to identify and evaluate the risk factors. This effort further defines the selected facility types by documenting the most common characteristics of the locations where crashes occurred. For example, if the previous tasks suggested a focus on road departure crashes on rural two-lane segments, this task might reveal that these crashes are overrepresented on roads that have a curvilinear alignment, poor road edges, and a specific range of traffic volumes. The two previous tasks relied on data typically available in crash records systems, as reported by law enforcement. The task of evaluating risk factors, however, generally requires road and intersection inventories to provide additional levels of detail. In situations where such inventories are unavailable, the Systemic Safety Project Selection Tool provides more information on how States can identify risk factors using video logs, online aerial imagery, or windshield surveys.
Step 2. The next step is to screen and prioritize locations that could benefit from systemic safety improvement projects. This involves conducting an assessment of the roadway elements for the focus facilities identified in step 1 to determine the presence (or absence) of the contributing risk factors at each location. The more risk factors present may indicate a higher risk and, therefore, a higher priority location for safety investments. The outcomes of this step are a risk assessment and rating of the focus facility types.
Step 3. The third step involves assembling a comprehensive list of potential countermeasures and evaluating each one to narrow the list down to a select few high-priority strategies targeting the focus crash type on the prioritized network elements. Given that the systemic approach involves deploying strategies widely, the selection process focuses on countermeasures that are low cost and proven effective. This step yields two key outcomes: (1) a short list of effective, low-cost countermeasures for each focus crash type that will become the target of the safety projects that follow; and (2) documentation of important characteristics of each strategy, such as whether it is tried and proven, expected effectiveness, estimated implementation and maintenance costs, and consistency with an agency’s policies and practices.
Step 4. The final step in element 1, conducting a systemic safety analysis, is deciding on the list of safety improvement projects using the prioritized at-risk locations identified in step 2 and the final countermeasures selected in step 3. To provide a measure of consistency in assigning countermeasures for widespread deployment, engineers may want to use a simple set of criteria considering factors such as traffic volume, environment, adjacent land uses, or roadway cross sections. Unlike the traditional site analysis approach to safety planning, which identifies the single best countermeasure for each individual location, the systemic approach considers multiple locations with similar crash and risk characteristics, and selects a preferred set of countermeasures suitable and affordable for widespread implementation. The primary outcome of this step is the identification of one or more countermeasures for each of the at-risk candidate locations along a system of roadways. Together, the individual projects comprise the jurisdiction’s systemic safety program.
The new element in the selection process is using the risk factors as a surrogate for severe crash experience. Agencies that have networks with low crash densities can rely on the risk factors to improve locations proactively, before a severe crash occurs, rather than reacting and implementing projects after someone is killed or severely injured.
Before moving on to the second element, it might help to look at a pilot test of conducting a systemic analysis to clarify the process. One of the strengths of the systemic process and the use of risk factors is that an agency can easily adapt the analysis to work with its available data. In a pilot test, the Kentucky Transportation Cabinet, New York State Department of Transportation, and Thurston County Public Works Department in Washington State each selected a similar focus facility and crash type, but used different risk factors to select priority locations. Despite choosing similar facility and crash types, the process used to evaluate and select risk factors varied across the three agencies.
Kentucky. The Kentucky Transportation Cabinet applied the systemic approach to 175 miles (280 kilometers) of county roadway (facility type) in six counties with a focus on road departure crashes (crash type) along horizontal curves. Staff from the University of Kentucky provided technical assistance with the identification and evaluation of risk factors, including traffic volume, access density, curve density for critical radius curves, presence of advance signing, intersections in the curves, and visual traps (where a crest vertical curve occurs before the beginning of the horizontal curve or when a minor road, tree line, or line of utility poles continues on a tangent). At the curves identified for safety improvements, Kentucky officials expect to assist the counties by deploying chevrons to delineate the curves.
New York. The New York State Department of Transportation applied the systemic approach by beginning with an analysis of the entire State roadway system for the purpose of identifying where specific crash types were occurring. Statistics on fatal and severe crashes were summarized using data from the State’s Safety Information Management System, roadway inventory system, and geographic information system for the years 2007–2011. Researchers summarized the data based on jurisdiction and type of crash. The data showed that 30 percent of the crashes statewide were on the State system, 45 percent on the local system, and 10 percent on the county system. The remaining 15 percent were on other facilities such as parking lots, private roads, or unknown locations. The data also showed that lane departures were the most prevalent type of crash on the State system, accounting for 30 percent of crashes. Of those, approximately 37 percent took place on rural, undivided roadways.
A further analysis of the data revealed characteristics or risk factors common among a high proportion of the lane departure crashes. The risk factors analyzed included number of lanes, speed, traffic volume, shoulder width, lighting conditions, and curve radius. The highest incidents of lane departure crashes were shown to occur on rural, two-lane, undivided roads with a traffic volume between 3,000 and 6,000 vehicles and a posted speed limit of 55 miles per hour (88 kilometers per hour), and shoulder widths between 1 and 3 feet (0.3 and 0.9 meter). Curves with a radius of less than 300 also had a high proportion of crashes on these roads. New York is exploring the use of larger chevrons and true wet reflective pavement markings to improve safety at rural curves.
In addition, New York is using a systemic approach to improve roadway safety by placing centerline audible roadway delineators along approximately 3,000 miles (4,800 kilometers) of roadway over the next 5 years and installing pedestrian countdown timers to improve safety at intersections. The current HSIP program aims to spend 70 percent of the funding on site-specific projects and 30 percent on systemic projects.
Washington State. Thurston County applied the systemic process to determine that road departure crashes (crash type) were the most common along county arterial and collector roads (facility type). According to county staff, there are 365 miles (587 kilometers) of county arterial and collector roads. In addition, the county determined that 45 percent of severe crashes occurred along horizontal curves. County officials identified numerous potential risk factors but ultimately selected five for the risk assessment: speed differential, visual trap, intersections, presence of advance warning signs, and edge assessment.
Next, the county identified optional countermeasures, selected criteria for priority locations, and prepared an investment strategy using a prioritization and selection process similar to the one presented in FHWA’s tool. Then the county applied for and received funding from the Washington State Department of Transportation to implement the countermeasures identified in the analysis. The installation of the countermeasures, including enhanced signing, rumble strips, delineators, and striping, is scheduled for summer and fall 2013.
"The systemic analysis is not driven by a particular crash at a particular location,” says Scott Davis, the traffic engineering and operations manager for Thurston County Public Works in Washington. "Instead, the county has a proactive tool for planning and implementing low-cost safety countermeasures for signed horizontal curves. The county now can help our constituents by ‘doing something’ before the crashes occur. We cannot drive deaths to zero if we keep waiting for something to happen.”
The systemic component of a highway safety program requires an agency to determine how to divide its safety investments among projects identified through the traditional site analysis approach and projects identified through the systemic risk assessment.
Exactly how to distribute the safety investments among candidate projects remains at the agency’s discretion. For example, if an agency has many black spot locations -- those with a high number of crashes -- on its system, the agency might choose to direct more of its safety funds to site analysis projects. However, if road departure crashes are the target crash type, and if rural county highways are the priority facility type, the agency might opt to allocate a greater percentage of safety funds to systemic projects.
In 2009, the Minnesota Department of Transportation (MnDOT) began directing approximately 65 percent of HSIP funding to county roads. For the rural counties, the goal was to make at least 70 percent of these safety investments in systemic projects. However, the State was able to direct nearly all local safety funds to systemic investments.
"Minnesota recognized in our strategic highway safety plan that engaging counties was essential to significantly reducing the number of fatalities,” says Sue Groth, MnDOT’s State traffic engineer. "Identifying funding goals, including an emphasis on systemic projects for our rural counties, has been instrumental in reducing fatalities and saving lives. Through the systemic approach, more than $31 million has been invested in safety improvements on local roads.”
The systemic approach provides program managers with the flexibility to respond to the needs of their roadway networks. After distributing funds and implementing projects, the managers can evaluate the projects and determine if the results are consistent with expectations. Are severe crashes trending downward, indicating a positive result? If the results of the safety investment were effective, the premise moving forward would be to continue on the same track. If the results were not in line with expectations, then the managers could consider a different distribution of safety investments.
Performance evaluation provides useful feedback for decisionmaking and is an important part of the overall process to reduce the number of fatal and serious injuries resulting from crashes. Like systemic safety programs themselves, the practice of evaluating the effectiveness of these programs is relatively new and evolving. Implementing countermeasures in locations that have no recent crash history but exhibit other characteristics that indicate the potential for a severe crash carries challenges when it comes to performance evaluations, especially for specific locations or corridors. The primary challenge is that implementation is based mainly on risk factors and historical crash experience. Therefore, the key is to evaluate at a program level, not individual project sites.
|This two-lane rural road in Thurston County, WA, shows roadside features and horizontal and vertical roadway alignments typical in the county.|
The Missouri Department of Transportation (MoDOT) recently applied the systemic process to low-volume paved roads in its State roadway system (facility type) and evaluated the results. Specifically, the State used a systemic implementation of edge lines for low-volume roads. "The systemic process identified the fraction of our system that was most at risk,” says John Miller, MoDOT traffic safety engineer. "An evaluation across the entire system of improved corridors, rather than individual locations, demonstrated the potential for a net benefit from the investment.”
Previously, MoDOT did not paint edge lines along the approximately 18,500 miles (29,770 kilometers) of these roads with traffic volumes less than 1,000 vehicles per day. However, analysis determined that the primary crash type (road departure) could be reduced with the addition of edge lines.
MoDOT’s approach used traffic volume as the primary risk factor and determined that the majority of fatalities and serious injuries -- approximately 570 per year -- occurred along approximately one-third of the segments that had traffic volumes between 400 and 1,000 vehicles per day. A preliminary evaluation of the edge lines focused on the performance across the majority of eligible routes, 570 centerline miles (917 kilometers) that were subject to the safety improvement in 2009 within the Central District. Looking at the system of improved roads, instead of individual locations, the evaluators found that total crashes dropped by 15 percent (statistically significant at the 95-percent level), and serious crashes declined by 19 percent (not significant at the 90-percent level).
|This sample crash tree for Minnesota county roads shows that local roads—county, city, and township—account for more than half of severe crashes. On county roads, with 1,963 severe crashes in 5 years, the majority of crashes were road departures that occurred on rural segments. Further, most of these crashes occurred at horizontal curves.<|
Minnesota and Missouri pioneered the systemic approach and have completed the four-step planning process, resulting in the identification and implementation of safety projects using the risk assessment technique. MnDOT’s application of the systemic process for county roads is unique in both the scale of the study and also for the fact that the State DOT performed the analysis for local agencies.
MnDOT applied the systemic approach in the preparation of safety plans for each of Minnesota’s 80 rural counties, which had received virtually no safety investment based on the traditional site analysis approach. The genesis of this effort was MnDOT’s strategic highway safety plan, which identified that approximately 50 percent of severe crashes in the State occurred on the 45,000-mile (72,420-kilometer) county system. Responding to a commitment in Minnesota’s strategic highway safety plan to engage the counties in improving safety, MnDOT added a systemic component to its Highway Safety Improvement Program to fund projects on county roadways. The department also provided technical assistance to conduct the risk assessment of each county’s system of roadways.
MnDOT applied the risk assessment in 80 rural counties on nearly 25,000 miles (40,233 kilometers) of rural paved county roads (facility type), which accounted for more than 80 percent of the severe crashes on local roads. Based on the crash data, MnDOT evaluated the counties’ 18,600 horizontal curves (facility type) to address the prevalent road departure crashes (crash type). In addition, department officials evaluated 12,000 rural through/STOP-controlled intersections, which accounted for approximately 30 percent of the severe crashes.
Because of the extremely low density of severe crashes (all rural segments, curves, and intersections averaged less than one severe crash per year), the risk factors used to prioritize these facilities included an evaluation of the road edge, traffic volume, and access density (number of entrances or exits to a street or highway per mile) for roadway segments. For curves, the risk factors included radius and the presence of visual traps. For intersections, the risk factors were skew, presence of commercial development, and proximity to the previous STOP sign. The selected priority safety strategies included enhanced road edges with rumble strips and 6-inch (15.2-centimeter) edge lines, enhanced curve delineation (chevrons), and upgraded traffic signs and streetlights for intersections.
In Minnesota’s seven urban counties, the assessment focused on 1,300 miles (2,092 kilometers) of urban road-ways and approximately 2,800 intersections. Crash analyses identified angle crashes and conflicts involving pedestrians and bicyclists at signalized intersections as the target crash types. The selected priority strategies to improve safety included advance confirmation lights to assist in enforcement to curtail red-light running and the addition of an advance walk interval (which allows the pedestrian to begin crossing before the vehicle traffic on the parallel street is given the green light) and countdown timers at crosswalks.
The systemic process identified more than $235 million in safety projects for implementation along Minnesota’s county highway system. Already, the State has implemented $31 million in projects funded by its Highway Safety Improvement Program.
Is your agency ready to adopt the systemic safety approach? FHWA’s Office of Safety recently launched a Web site (http://safety.fhwa.dot.gov/systemic) that provides information for agencies looking to initiate or expand implementation of a systemic safety approach. Users can download the Systemic Safety Project Selection Tool and other resource documents from the site.
The site also includes information on the benefits and challenges associated with the systemic approach and step-by-step instructions, with examples, to guide users through the planning process. Other features include a discussion of risk factors associated with particular crash types and roadway characteristics, as well as case studies demonstrating the application of the systemic approach. Further, agencies can submit their own noteworthy practices to FHWA’s online database through the site.
|Where this paved road meets a rural road at a horizontal curve creates what safety engineers call a visual trap. The gravel road, from this perspective, gives the false perception that the paved road continues straight, when in fact it curves to the left.|
"The systemic approach to safety allows us to proactively address safety on our county road system,” says Brian Roberts, executive director of the National Association of County Engineers. "We will continue to address our high-crash locations, but the systemic approach to safety provides a mechanism to widely deploy countermeasures across the county road system using a systematic, data-driven process.”
Howard Preston, P.E., is a principal traffic and safety engineer with CH2M HILL in Mendota Heights, MN. He has a B.S. in civil engineering from Iowa State University.
Richard Storm, P.E., PTOE, is a project engineer working in traffic operations and safety with CH2M HILL. He has an M.S. in civil engineering from Iowa State University.
Karen Scurry, P.E., is the Highway Safety Improvement Program manager with FHWA’s Office of Safety. She has an M.S. in civil engineering from Rutgers, the State University of New Jersey.
Elizabeth Wemple, P.E., is a senior associate at Cambridge Systematics. She has 20 years of experience as a transportation planner and traffic engineer, focusing on roadway safety management for State and local jurisdictions.