Citation

Kononov J, Durso C, Lyon C, Allery B. Transp. Res. Rec. 2015; 2514: 10-20.

Copyright

(Copyright © 2015, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

10.3141/2514-02

PMID

unavailable

Abstract

The concept of the level of service of safety (LOSS) was developed at the Colorado Department of Transportation in 2000. LOSS reflects how a roadway segment or an intersection is performing in reference to the expected frequency and severity of crashes predicted by its safety performance function. The LOSS concept provides quantitative assessment and qualitative description of the degree of safety of a segment or an intersection. In addition, the loss concept facilitates effective communication about safety problems to other professionals, the traveling public, and elected officials. The LOSS concept was first introduced in a paper titled "Level of Service of Safety: Conceptual Blueprint and Analytical Framework," published in 2003 in the Transportation Research Record: Journal of the Transportation Research Board, No. 1840. LOSS was incorporated into the first edition of the AASHTO Highway Safety Manual and is used by the Departments of Transportation of Colorado, Louisiana, Montana, Oklahoma, and Wyoming and the Ontario Ministry of Transport, in Canada. LOSS lends itself well to the safety decision-making process in departments of transportation. However, the concept did not initially address correction for the regression to the mean bias. A new method is introduced for using LOSS in concert with correction for regression to the mean bias with an empirical Bayes procedure. In addition, distributional assumptions associated with LOSS are revisited, how the LOSS boundaries are calibrated in the population corrected for the regression to the mean bias is explained, and an intuitive percentile-based reporting method is provided. Finally a diagnostic example and a before-and-after study demonstrating the value of LOSS in identifying the safety problem at a real location are worked through.