U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
In the day-to-day operation and management of the transportation system, agencies are responsible for providing a safe and efficient transportation system for users. Within this context, the term operations refers to the use of programs, technology, and business processes to support the flow of vehicles, travelers, and goods on the existing transportation infrastructure (FHWA, 2012a). Operations include asset management; activities and technologies for managing and minimizing recurring congestion; reducing the risk and extent of nonrecurring congestion; managing incidents, weather events, construction work zones, or special events; integrating freight mobility and capacity needs into the system; and managing and mitigating day-to-day traffic operations as appropriate at intersections, and along roadway segments.
The HSM offers data-driven and science-based methods and tools that can be used to monitor and identify treatments likely to improve the safety performance of the roadway network. The following items represent typical applications:
The remainder of the section presents a discussion of each of these applications alongside applicable tools and HSM references.
Chapter 4 of the HSM presents a number of alternative measures to quantify safety performance. While the HSM does not identify particular performance measures as preferred approaches, the manual outlines the strengths and limitations associated with each. Such information can be particularly useful in the selection of one or a combination of performance measures agencies use to quantify safety performance. While, crash frequency (from crash history) and crash rates were traditionally used as performance measures, the HSM presents performance measures with a higher reliability than these measures. Using a higher reliability performance measure increases the likelihood that locations most likely to benefit from safety treatments are selected for further evaluation.
Using Part B of the HSM, agencies can measure the safety performance of corridors, segments and intersections using any one or a combination of the performance measures in HSM Chapter 4. A safety performance assessment may represent an annual or tri-annual assessment alongside other performance assessments, such as operational conditions (recurring congestion, nonrecurring congestion, etc.), pavement conditions, or bridge conditions. Using these results, agencies can apply approaches discussed in HSM Chapter 5 to diagnose site and crash characteristics. Agencies can use HSM Chapter 6 to identify likely countermeasures that can be considered to reduce overall crash severity. Once countermeasures are identified, the methods in Chapter 7 of the HSM can be used to assess the economic costs and benefits associated with each alternative. After an assessment of other impacts associated with each of the alternatives (e.g., environmental, public acceptance, and legislative framework) agencies can identify and implement the treatment or group of treatments at the particular location or group of locations. Chapter 8 of the HSM includes methods that an agency can use to prioritize a set of locations for treatment – a typical approach to support decision-making within a particular program or financial year.
Within operations, agencies often consider a collection of sites for typical improvements based on similarity of characteristics and particular operational needs. These treatments may vary in cost and operational impact. The HSM methods allow an agency to also include safety performance as criteria for selecting the sites and identifying treatments, particularly where the crash experience suggest potential for safety improvement. Part D of the HSM or information from the FHWA CMF Clearinghouse may provide insight as to the safety impact of operational-based changes. Examples may include, conversion of signalized intersections into roundabouts, change in signal change intervals, changes in signal phasing (e.g., changing permissive to protected-permissive phasing, changes to phasing to a protected-permissive phasing with flashing yellow arrow for the permissive phase). When operational treatments also represent systemic safety treatments, implementation often offers a relatively low-cost solution to lower fatal and serious injury risk on the system.
Decisions in operations and maintenance often include assessments of anticipated changes in performance for different operational and site characteristics. The HSM and related tools allow an agency to assess the change in safety performance (measured in crash frequency and severity) due to operational changes. For example, on high-volume freeway corridors shoulder running may be under consideration as a traffic management strategy. Forthcoming HSM freeway research results provide information about the quantitative safety impacts of such operational changes. With the use of the HSM predictive method (and in this case the anticipated additional chapter on freeway safety prediction) agencies can quantify the relative change in crash frequency and severity for such alternatives. Part D of the HSM and the FHWA CMF Clearinghouse provide information for a variety of such alternatives.
Chapter 9 of the HSM presents state of the practice methods in safety performance evaluation. These methods include methods that are associated with higher reliability than traditional approaches.
Once an agency implements operational changes to corridors or sites, Chapter 9 in the HSM can be used to incorporate safety into monitoring activities at these treated sites. Results from these evaluations may serve as input to accountability reports to the legislature and public.
Past evaluations for safety consisted of naive before-after studies, in which the crash performance before implementation is compared to the crash performance after implementation. The more advanced methods in Chapter 9 of the HSM offer particular value in that they improve the reliability of results compared to the traditional approach. Some of these methods, (e.g., the empirical Bayes method with comparison sites) also allow an agency to control for systemwide changes that may be difficult to detect otherwise.
Agencies often have to make trade-offs between funding maintenance improvements to such items as pavement, roadside facilities (e.g., guardrail, signs, lighting), and bridge facilities. The HSM provides tools (i.e., crash modification factors, and the predictive method) to quantify the effects of maintenance decisions on changes in crash frequency or severity on the transportation system. This information could be extended to a benefit/cost analysis using methods from Part B of the Highway Safety Manual.
