Study Details
Study Title: An Empirical Bayes before-after evaluation of road safety effects of a new motorway in Norway
Authors: Elvik et al.
Publication Date:SEP, 2017
Abstract: This paper presents an Empirical Bayes before-after evaluation of the road safety effects of a new motorway (freeway) in Østfold county, Norway. The before-period was 1996–2002. The after-period was 2009–2015. The road was rebuilt from an undivided two-lane road into a divided four-lane road. The number of killed or seriously injured road users was reduced by 75 percent, controlling for (downward) long-term trends and regression-to-the-mean (statistically significant at the 5 percent level; recorded numbers 71 before, 11 after). There were small changes in the number of injury accidents (185 before, 123 after; net effect −3%) and the number of slightly injured road users (403 before 279 after; net effect +5%). Motorways appear to mainly reduce injury severity, not the number of accidents. The paper discusses challenges in implementing the Empirical Bayes design when less than ideal data are available.
Study Citation: Elvik, R., H. Ulstein, K. Wifstad, R.S. Syrstad, A.R. Seeberg, M.U. Gulbrandsen and M. Welde. "An Empirical Bayes before-after evaluation of road safety effects of a new motorway in Norway". Accident Analysis and Prevention, Vol. 108, (2017) pp. 285-296.
Study Report: Download the Study Report Document
CMFs Associated With This Study
Category: Roadway
Countermeasure: Convert 2-lane undivided to 4-lane divided road
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.971 | 2.9 |  | All | K,A,B,C,O | Not specified | All |
| 0.251 | 74.9 |  | All | K,A | Not specified | All |
| 1.05 | -5 | | All | B,C | Not specified | All |
