Overview of SafetyAnalyst Software

SafetyAnalyst is a set of computerized analytical tools being developed for the Federal Highway Administration to assist state and local highway agencies in highway safety management. The main purpose of SafetyAnalyst is to improve a highway agency’s systemwide programming of site-specific safety improvements. SafetyAnalyst applies advanced statistical techniques for safety management in four main analytical tools: Network Screening, Diagnosis and Countermeasure Selection, Economic Appraisal and Priority Ranking, and Countermeasure Evaluation. This paper presents a general overview of the SafetyAnalyst program features. The Network Screening tool includes six algorithms to identify sites with potential for safety improvement: peak searching for high accident frequencies, sliding window for high accident frequencies, high proportion of target accident types, steady increase in accident frequency, sudden increase in accident frequency, and corridor analysis. This tool uses traditional screening techniques as well as new statistical methodologies such as the empirical Bayes (EB) approach. The Diagnosis and Countermeasure Selection tool enables users to investigate the nature of safety concerns at specific sites through accident summary statistics, collision diagrams, and statistical tests for specific accident patterns. Through the use of an expert system, this tool also assists users in the diagnosis of specific accident patterns as well as the identification and selection of countermeasures that address these specific accident patterns. The Economic Appraisal and Priority Ranking tool performs economic appraisals of alternative countermeasures for a specific site or group of sites. Several economic criteria are available for use within SafetyAnalyst: cost-effectiveness, benefit-cost ratio, or net present value. This tool also provides the ability to determine an optimal set of countermeasures for a group of sites that will maximize the safety benefits of the improvements with a user-specified improvement budget. The Countermeasure Evaluation Tool provides the ability to conduct well-designed before-after evaluations of implemented safety improvement projects. Two statistical approaches are provided for such evaluations: an EB approach for determining changes in accident frequencies and a nonparametric test for shifts in the proportions of specific accident severity levels or accident types.