Transverse rumble strips (TRS) (also called in-lane rumble strips) have been used by some agencies in rural areas to warn drivers that they are approaching a stop sign. There is some evidence in prior research that TRS are effective in reducing approach speeds. However, little is known about effects on crashes since the results from the past crash based studies are not reliable. This study was an attempt to add to the knowledge of crash effects.

Data from 20 intersections in Minnesota and 134 intersections in Iowa were used to examine the safety impact of TRS at three and four-leg intersections with minor-leg stop-control. Empirical Bayes methods were incorporated in a before-after analysis to determine the safety effectiveness of the rumble strips, while accounting for potential selection bias and regression-to-the-mean effects. Results from 3- and 4-leg intersections in the combined sample of Iowa and Minnesota indicate about a 21 percent reduction in KAB crashes and a 39 percent reduction in KA crashes. Coupled with this reduction in severe injury crashes, there seems to be an increase in PDO crashes.

While it was not possible to determine the reasons for this tradeoff, a limited economic analysis indicated a reduction in crash harm of about $6,600 per intersection per year due to the installation of TRS. Due to limited sample sizes, no definitive conclusions could be made regarding the specific crash types investigated, i.e., right angle and ran-stop-sign crashes.