The SafetyAnalyst toolkit will include six software programs to help transportation agencies analyze the safety performance of specific sites, suggest appropriate countermeasures, quantify their expected benefits, and evaluate their effectiveness.
Network Screening Tool
The network screening tool will help users identify potential sites for safety improvements. Algorithms will identify:
- Sites with higher-than-expected crash frequencies that may indicate the existence of safety problems that are correctable in a cost-effective manner.
- Sites where crash frequencies are not higher than expected but that experience enough crashes to warrant cost-effective measures to improve highway safety.
The network screening tool also will identify sites with a high number of severe crashes and high levels of specific crash or collision types and identify extended roadway segments as potential sites for corridor- or route-based improvements.
This tool will help users understand the nature of problems at specific sites. The tool will generate collision diagrams to identify the predominant collision patterns and assess whether these patterns represent higher-than-expected frequencies of particular collision types. The tool also will guide users through office and field investigations to identify safety concerns at the specified location. The diagnosis tool will help users consider both traditional engineering criteria and human factors needs. The result will be the identification of existing crash patterns and a list of safety concerns that could potentially be mitigated by countermeasures. The diagnosis tool also will include a basic collision diagramming capability and will be able to interface with select commercially available collision diagramming software packages, including collision diagramming software with interactive capabilities.
Countermeasure Selection Tool
The countermeasure selection tool will focus on the selection of appropriate countermeasures to mitigate the crash patterns identified by the diagnosis tool. The tool will help users identify candidate improvements that address the safety concerns at a particular site. In addition, the tool will recommend potential countermeasures pertinent to each diagnosis, and the user will be informed of which countermeasures under consideration have known and reliable effectiveness measures, such as accident modification factors (AMFs). Users will be able to tentatively select specific countermeasures (or combinations of countermeasures) for potential implementation, subject to the results of an economic analysis.
Economic Appraisal Tool
This tool will perform three types of economic appraisals of proposed countermeasures: cost-effectiveness, benefit-cost ratio, and net present value analyses. To estimate the safety effectiveness of potential countermeasures, the tool uses data on crash frequency and severity and crash patterns along with AMFs. Analyses will include consideration of the service life of each countermeasure and the time value of money. The tool also will be able to conduct evaluations that are consistent with the requirements of the Federal Highway Administration’s (FHWA) Highway Safety Improvement Program so results can be implemented using Federal funds.
Priority Ranking Tool
This tool uses the results of the economic appraisals to ranks sites and proposed improvement projects. To develop the ranking, the tool compares the benefits and costs of countermeasures across sites, and then ranks projects based on their cost effectiveness, benefit-cost ratio, or net present value. The rankings enable users to decide whether to fund projects based on their priority measure. In addition, users will be able to use an optimization tool to select a set of countermeasures that maximizes the safety benefits of an improvement program within a specific budget.
This tool will enable users to conduct before and after evaluations of safety improvement projects. These evaluations are important to increase knowledge of project effectiveness and to refine the safety measures available in SafetyAnalyst. The primary statistical approach to before and after evaluation will be the Empirical Bayes technique.