by Matt Mann, Research Program Coordinator
Centerline rumble strips have been shown to reduce lane departure crashes by as much as 25% on rural roads, and are now being installed on undivided, rural, two-lane highways in Massachusetts as appropriate.
Improving safety, at a low-cost, can reduce crashes and save lives. In the U.S., 60% of crashes on rural roads result in a fatality. Of these fatal crashes, approximately 90% are on two-lane roads. Lane departure crashes from vehicles crossing over the centerline on undivided, two-lane, rural roads have been proven to decrease with the installation of centerline rumble strips (CLRS). This reduction can be as high as 25% along certain rural roads, and even higher when CLRS are installed along with shoulder rumble strips (SRS).
Many factors contribute to drivers crossing over the center yellow line, including speeding, fatigue, and drowsiness, and distracted driving. Some common techniques on the roads now that try to mitigate lane departures and improve safety include, but are not limited to centerline and edge line pavement lane markings, higher retroreflectivity of traffic signs (for day and nighttime visibility), and vertical reflective panels. All of these have had some success. A number of studies, however, have shown CLRS to be more effective along certain rural sections of highways, in decreasing lane departures.
The purpose of CLRS is to prevent vehicles from crashing head-on or sideswiping each other. Vehicles tend to veer outside of their lane on all types of roadways, especially on undivided, two-lane rural highways where cross-over crashes are most common. CLRS can also act as a traffic calming tool. Similar in design to the rumble strips on the shoulders of Interstates and other limited access highways, CLRS are located along the centerline. With either placement, the objective of the rumble strips is to alert inattentive drivers that they are veering outside of their lane, and ideally help them correct this action before a crash occurs.
The main reason for CLRS’ effectiveness is their design, specifically the vibrations and noise when tires cross over them. However, this noise has also been a major reason why CLRS are not used on more roads. Abutters and businesses have complained about CLRS being too loud as vehicles cross over them. California Department of Transportation (CalTrans) and Minnesota DOT (MnDOT) have conducted research on creating effective, quieter CLRS. MnDOT has developed the sinusoidal wave-shaped rumble strip. Some study results have shown a decrease in noise levels outside the vehicle, as vehicles cross over these sinusoidal rumble strips, while the CLRS still maintain the effectiveness by alerting drivers of lane departures. In addition to noise, another concern of CLRS is the potential reduction of visibility of the centerline yellow strip, though, in a survey by the Insurance Institute for Highway Safety, some respondents reported that the visibility of the centerline yellow strip in the rain was better over CLRS than on flat pavement.
MassDOT, along with other DOTs, continues to develop and implement CLRS on their rural, undivided, two-lane highways. MassDOT currently considers implementing CLRS on an as needed basis. Decisions about where to install CLRS are based on a couple of variables, including lane departure crash data and land use (regarding the noise factor). As discussed with Bonnie Polin, MassDOT Highway Division Manager of Highway Safety, CLRS were recently included in a paving project along sections of Route 140 in Gardner and Winchendon. CLRS are easier and more cost effective to install when a roadway is being re-paved as was the case along Route 140. As MassDOT updates its Strategic Highway Safety Plan, CLRS are referenced as a safety measure to prevent lane departures. MassDOT will continue to support and install CLRS on their secondary roads, where appropriate.