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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2020. Guide for Quantitative Approaches to Systemic Safety Analysis. Washington, DC: The National Academies Press. doi: 10.17226/26032.
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1 Guide for Quantitative Approaches to Systemic Safety Analysis Highway agencies have traditionally managed their highway safety improvement process by identifying and correcting high-crash locations (“hot spots”) where concentrations of crashes and/or patterns of crashes were found. Recently, to complement their crash- history-based safety management approach, highway agencies have incorporated a systemic safety management approach within their Highway Safety Improvement Program (HSIP). The systemic safety management approach is used to program implementation of safety treatments at sites that reduce the potential for crashes using crash prediction models or rating systems to estimate relative crash potential or the opportunity to reduce crashes. The systemic safety management approach is intended to address crash types that occur with high frequency across the roadway network but are not concentrated at individual locations, which tend to be overlooked when ranking sites using a crash-history-based safety management approach. Benefits of Systemic Safety Management The potential benefits of implementing a systemic safety management approach include the following: • It can be used in the absence of high-quality historical site-level crash data. • It is proactive because countermeasures can be programmed for implementation at locations that may not have a history of crashes. In particular, even sites with zero crash history can be identified for potential safety improvement using a systemic safety management approach. • It helps agencies broaden their traffic safety efforts and consider the potential for future crashes and crash history when identifying where to make safety improvements. • It provides the ability to program projects further into the future as projects can be based on the presence or absence of crash contributing factors (i.e., roadway characteristics) that do not change frequently from year to year. • It may be easier to more equally distribute safety funds regionally or across jurisdictions. • It is adaptable based on available data. Primary Approaches to Systemic Safety Management Systemic safety application looks very different from one agency to the next. In general, three primary approaches have been used to implement systemic safety management: • Application of the FHWA Systemic Safety Project Selection Tool methodology, customized to local data availability and program goals. S U M M A R Y

2 Guide for Quantitative Approaches to Systemic Safety Analysis • Application of safety performance functions (SPFs) using in-house analysis tools or Safety Analyst software. • Application of the U.S. Road Assessment Program (usRAP) methodology, using the asso- ciated ViDA software. Common Focus for Systemic Approach Common crash types that agencies have addressed using a systemic safety management approach include: • Lane departure, • Rollover, • Fixed object, • Head-on, • Angle, • Speed-related, • Younger driver involvement, • Impaired driving, • Pedestrians, • Bicyclists, and • Nighttime. In conjunction, several facility types that agencies have focused on using systemic safety management approaches to address target crash types include: • Rural freeways, • Rural multilane highways, • Rural two-lane roads, • Rural local roads, • Rural roads with pavement width less than 24 ft, • Horizontal curves on rural two-lane roads, • Low-volume local roads, • Unpaved roads, and • Signalized and stop-controlled intersections. Types of countermeasures that agencies have implemented as part of their systemic safety management projects include: • Roadway segments: – Rumble strips (both shoulder and centerline), – Cable median barrier, – SafetyEdge, – High friction surface treatments, – Enhanced pavement markings, – Curve warning signs, – Chevrons/delineators, – Lane/shoulder widening, – Speed feedback signs, – Tree/clear zone removal. • Intersections: – Signal backplates, – Crosswalk enhancements—striping, signing, rectangular rapid flashing beacons, – Countdown pedestrian signals, – Pedestrian refuge islands,

Summary 3 – Curb extensions, – Reflective strips on sign posts, – Mini-roundabouts, – Lighting. Implementation The systemic safety management approach is adaptable based on available data, but its implementation may still be relatively data-intensive, potentially incorporating reliable roadway inventory, traffic volume, and/or crash data. When implementing the FHWA Systemic Safety Project Selection Tool methodology, agencies utilize available data sources but in most cases, still collect additional data elements to identify crash contributing factors for focused crash or facility types. Crash contributing factors are identified by evaluating which factors are overrepresented in severe crashes; therefore, larger datasets with multiple counties or jurisdictions may be necessary to establish a large enough sample size of road- way segments/intersections and crashes to determine overrepresentation. Contributing factor determination can be somewhat subjective, requiring some expertise and familiarity with the methodology and a thorough understanding of the state of the roadway network being analyzed. When implementing systemic safety using SPFs, roadway inventory, traffic volume, and crash data are required to develop jurisdiction-specific SPFs and/or calibrate existing SPFs. To implement systemic safety using SPFs, most agencies develop their own in-house tools. If an agency wants to use Safety Analyst to implement systemic safety, this software requires approximately 40 data elements to utilize the full functionality of the software. Most of the “required” data elements are Fundamental Data Elements (FDEs) as designated within the Model Inventory of Roadway Elements (MIRE). States are required to have access to a complete collection of the MIRE FDEs on all public roads by September 30, 2026. Most agencies are working to collect these MIRE FDEs but may not currently have all of the required data elements to make full use of the Safety Analyst functionality and capabilities. Agencies can still use Safety Analyst if they do not have all of the required data elements, but the analyses will be limited to the facility types and network for which all of the required data elements are available. To apply the usRAP methodology using the associated ViDA software requires use of over 50 roadway characteristics to develop star ratings and estimate fatalities and serious injuries for individual roadway segments. The primary input data for the usRAP ViDA software can be coded from review of aerial photos and street-level photos of the site using highway agency photologs or web-based mapping tools. On average, it takes about 30 minutes of labor per mile for a trained coder to prepare the input data for a roadway. Coding tools are available to help prepare input data for use within the usRAP ViDA software. Evaluation Evaluation of systemic safety management programs can be conducted in a number of ways depending on the type and amount of data available, the goals of the evaluation, and the agency’s available resources in terms of time and expertise. Quantitative impacts of a systemic safety management program are most commonly analyzed using a trend analysis, a simple before-after study approach, a shift of proportions method, or the empirical Bayes before-after study method. Agencies have implemented each of these evaluation methods to inform future decision making to maximize the safety program and achieve goals.

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Traditional approaches to safety have focused on identifying high-crash locations and implementing projects to address predominant concerns at these locations. The systemic approach to safety is a method of safety management that typically involves lower unit cost safety improvements that are widely implemented based on high risk factors.

The TRB National Cooperative Highway Research Program's NCHRP Research Report 955: Guide for Quantitative Approaches to Systemic Safety Analysis provides guidance to state departments of transportation (DOTs) and other transportation agencies on how to apply a systemic safety management approach for identifying safety improvement projects.

Material associated with the report includes NCHRP Web-Only Document 285: Developing a Guide for Quantitative Approaches to Systemic Safety Analysis and a PowerPoint of the summary of project findings and future research needs.

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