Methodological guidelines for developing accident modification functions

Abstract

This paper proposes methodological guidelines for developing accident modification functions. An accident modification function is a mathematical function describing systematic variation in the effects of road safety measures. The paper describes ten guidelines. An example is given of how to use the guidelines. The importance of exploratory analysis and an iterative approach in developing accident modification functions is stressed. The example shows that strict compliance with all the guidelines may be difficult, but represents a level of stringency that should be strived for. Currently the main limitations in developing accident modification functions are the small number of good evaluation studies and the often huge variation in estimates of effect. It is therefore still not possible to develop accident modification functions for very many road safety measures.

Before–After Evaluation of the Realignment of Horizontal Curves on Rural Two-Lane Roads

“…This CMFunction could then be estimated as a regression equation. Elvik ( 20 ) recommended that the variance of the CMF needs to be considered in this estimation. The inverse of the variance is typically introduced as a weight in a weighted regression model.…”