Bridge Engineering Center

About the research

Retroreflective strips have been added to signposts, such as stop signs and curve chevron signs. The intent is to increase conspicuity of the sign. In particular, this countermeasure may be more effective during wet weather or low light conditions. It may be particularly beneficial to older drivers.

The countermeasure is low cost and easily applied. However, it does require maintenance and periodic replacement. As a result, additional information is needed to assess the safety impacts in order to assess the relative benefits. Development of a crash modification factor (CMF) comparing crashes before and during implementation of a countermeasure is the most robust method to evaluate effectiveness. The retroreflective strip countermeasure has been applied on a number of curve chevron signposts in Iowa and other locations. Most of these were installed three to five years ago. As a result, sufficient sites are present that will allow a before and after analysis to be conducted. Information about most of these sites (i.e., location, installation date) has already been captured. This will provide a unique opportunity to evaluate the effectiveness of this treatment