Safety interventions (e.g. median barriers, photo enforcement) and road features (e.g. median type and width) can influence crash severities, crashfrequencies, or both. Both dimensions-crash frequency and crash severity-are needed to obtain a full accounting of road safety. Extensive literature and common sense both dictate that all crashes are not "created"equal-with fatalities costing society nearly 400 times more than property damage crashes on average. Despite this disparity, the profession has not unanimously embraced or successfully defended a single severity weighting approachfor conducting safety analyses. This paper argues that the two dimensions (frequency and severity) are made available by intelligently weighting crash frequencies and converting all crashes to property damage only (PDO)crash equivalents using comprehensive unit crash costs. This approach is analogous to calculating axle load equivalents when predicting pavement damage-for instance a 40,000 lb truck causes 4025 times more stress than does a 4000 lb car and so simply counting axles is not sufficient. Calculating PDO equivalents using unit crash costs is the most defensible and non-arbitrary weighting scheme, allows for the simple incorporation of severity and frequency, and should be explored more thoroughly. Moreover, we show that using PDO equivalents diminishes the errors introduced by under-reporting of less severe crashes-an added benefit of the PDO equivalent analysisapproach. We demonstrate the method using rural road segment data from Korea. Finally, we discuss the results and remaining issues with PDO equivalents and their adoption in safety analysis.
Samenvatting