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Publication Number: FHWA-HRT-05-051
Date: October 2005

Crash Cost Estimates by Maximum Police-Reported Injury Severity Within Selected Crash Geometries

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INTRODUCTION

In conventional traffic safety evaluations, the outcome measure is typically the frequency of police-reported crashes, often with separate estimates for different severity levels. However, some treatments may decrease some crash types but increase others. If these crash types are characterized by different average injury severities, then comparing crash frequencies will not provide the user with an accurate picture of treatment effectiveness. Such a scenario led to the development of the crash cost estimates by crash geometry described in this report. An example of this scenario can be found in an evaluation of red-light camera (RLC) programs in seven jurisdictions nationwide funded by the Federal Highway Administration (FHWA) Intelligent Transportation System Joint Program Office and the Office of Safety Research and Development. RLC programs can be expected to decrease angle-type crashes, but to increase rear end crashes. The former is usually more severe than the latter. For that reason, the study not only examined crash frequency by type, but also included crash severity in the analysis by converting each crash to an economic cost, based on unit costs by police-reported crash severity. Similar procedures would be appropriate in the evaluation of such roadside hardware as median barriers, which would be expected to increase the number of less severe sideswipe and angle crashes into the barrier while decreasing or eliminating the more severe head-on crashes into vehicles in opposing lanes of traffic. Although many past studies developed crash costs (Miller, et al. 1997; Zaloshnja, et al., 2004),(1,2) most studies provide estimates per person injured or vehicle damaged rather than the cost per crash. Moreover, they often provide cost breakdowns by body region and within that by injury severity measured on the Abbreviated Injury Scale (AIS). AIS is specified by trained medical data coders, usually within a hospital context. It is not recorded on police crash reports, making these cost estimates unusable in the majority of safety studies conducted.

Miller et al.(1) successfully linked crash costs to police-reported crash profiles for a number of crash scenarios by using data files that contained both AIS and police-reported KABCO[1] severity (National Safety Council, 1990).(3) That study provided aggregate costs, not unit cost estimates by KABCO severity and crash type. It was intended to aid vehicle design that minimized overall harm. Wang et al. undertook a similar study, estimating unit costs by crash geometry and AIS for crashes that could be averted by Intelligent Vehicle-Highway Systems (IVS) technologies.(4)

This study builds on the prior studies, providing current unit costs by crash type and severity. Modifications of the previous work included:

  • Providing the human capital (economic) cost estimates of hard dollar consequences and comprehensive cost estimates that add the value of the nonmonetary losses to the economic costs for six KABCO groupings within 22 critical crash types (e.g., pedestrian crash at signalized intersection; multi-vehicle cross-path crash at unsignalized intersection) and within two speed limit categories to account for possible differences in cost for a given KABCO level between crashes in urban and rural locales.
  • Giving estimates for six different combinations of KABCO severity (e.g., each KABCO level, K+A versus B+C+O, all levels combined, etc.). These groupings facilitate use in studies where, for example, the sample size of fatalities is so small as to be unstable, and thus where one or two fatalities might bias the study results.

[1] The KABCO severity scale (National Safety Council, 1990) is used by the investigating police officer on the scene to classify injury severity for occupants with five categories: K, killed; A, disabling injury; B, evident injury; C, possible injury; O, no apparent injury. These definitions may vary slightly for different police agencies.

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