Rumble strips are commonly used on shoulders of roads, but since 1994 there has been a limited use of rumble strips on the centerline of highways. An analysis of these CLRS, done by an insurance industry group, the Insurance Institute for Highway Safety in September 2003, (see study) determined that these CLRS reduced crashes and concluded, "consideration should be given to installing centerline rumble strips more widely on rural two-lane roads to reduce the risk of frontal and opposing direction sideswipe crashes."
Caltrans has adopted a policy of installing these CLRS on its highways, as part of its safety program. Although studies have indicated a reduction in centerline drift crashes, no study has evaluated the effect of CLRS on bicyclist safety. At a meeting of the California Bicycle Advisory Committee in August 2008, a request was made that Caltrans institute a moratorium on installing CLRS until the safety implications for cyclists was determined; however, this request was denied, and Caltrans has an ongoing all-out project to install these CLRS on all rural state highways.
Bicyclist concerns revolve around the following issues:
1. The installation of a CLRS can reduce the lane width, thereby making a lane too narrow to share with vehicular traffic
2. When passing bicyclists on a narrow road, most motorists will straddle the centerline, allowing sufficient room for the bicyclist to continue to ride safely. Many bicyclists are concerned that the CLRS will inhibit motorists from crossing the centerline, and that they will attempt to squeeze pass bicyclists when passing. Many bicyclists have reported that motorists pass them with insufficient clearance, when CLRS are installed and there is no shoulder.
Caltrans has general policies that promote the use of bicycles, and that mandate that bicyclist safety be considered in road projects. If CLRS actually make bicycling less safe, or less comfortable, an have the effect of decreasing the number of cyclists on these roads, that would be against Caltrans policy. Unfortunately, we do not have before and after counts of bicyclists in most of these locations.
To help SVBC gather information on how this issue affects cyclists, please fill out our CLRS Survey.