Does the guidance recommend shoulder rumble strips only where a clear 4-foot surface is provided beyond the rumble strip?
No. The guidance recommends that shoulder rumble strips be installed on all roadways meeting certain criteria regarding speed, crash history, etc. The presence of a 4-foot shoulder is one of the listed criteria. So while the guidance recommends shoulder rumble strips where there is 4 feet or greater of shoulder beyond the strips, it does not recommend against rumbles where there is less than 4 feet. In those cases there are many issues for the responsible agency to consider, including whether the shoulder is used by bicyclists and therefore needs a specified amount of paved area beyond the rumble strip to accommodate them. Using the metric of 4-feet in the recommendation allows a practice that will work as a typical application, and accommodate cyclists. Use of shoulder rumble stripes can also maximize the width of shoulder available to bicyclists.
