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This report is an archived publication and may contain dated technical, contact, and link information
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Publication Number:  FHWA-HRT-14-081    Date:  November 2014
Publication Number: FHWA-HRT-14-081
Date: November 2014


Enhancing Statistical Methodologies For Highway Safety Research – Impetus From FHWA


Several notable experts with a combination of statistical and transportation safety research were asked to review the draft white paper and provide comments. These valuable reviews provided additional ideas. The scope of the body of the white paper is necessarily limited to ideas presented and discussed at the technical experts meeting, but the additional ideas generated by the reviewers are documented in this appendix in keeping with the objectives of the white paper. To maintain the anonymity of the peer review process these ideas are not attributed to any specific reviewer, although their contribution is acknowledged and appreciated.

Institutional Suggestions

Several comments were received with respect to the Institutional Suggestions section of this white paper and include the following:

Technical Approach Suggestions

A number of comments were received with respect to the Technical Approach Suggestions section of this white paper. These relate to other methodologies not discussed and issues not addressed.

Application of Interrupted Time Series Design and Generalized Linear Segmented Regression Analysis

An interrupted time series design is a quasi-experimental method used to determine the impact of an intervention. A generalized linear segmented regression analysis with time as a variable to control for overall trend and intervention as a variable to estimate the effect of the countermeasure is a statistical method for analyzing the data from the interrupted time series design.(15) Although this method has not yet been widely used in estimating CMFs and SPFs, it has a great potential to overcome some of the long-lasting problems in estimation of CMFs and SPFs in that it can account for time trends from before-after studies as well as can cope with a problem of defining reference/comparison group when treatment is universal. This method needs to be promoted and disseminated along with other new or enhanced methodologies.


Given that individual studies relating to transportation safety issues are often conducted with modest sample sizes, especially when they address countermeasure evaluations, meta-analysis based summary assessment of functional forms, parameter estimates, and results would be of great interest.

Additional Methods

Additional methods not mentioned but which may have relevance include the following:

Additional Issues



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