Rumble Strip - Continuous Shoulder Rumble Strips (CSRS)

Continuous Shoulder Rumble Strips (CSRS)

Montana undertook an extensive 10 year multi-site study of the effectiveness of CSRS on Interstate and primary highways (that are both divided). This study investigated the severity of accidents which sets it apart from previous studies. The results indicated a 14% reduction in accidents on Interstate highways; however the effectiveness on primary highways indicated both improvements and worsening and the results considered inconclusive. It was found that "roll-overs" decreased in number, but increased in severity. The study only considered accidents in dry and wet conditions, not snow and ice.

The FHWA undertook a multi-state study involving test sites from Illinois and California. The Illinois component indicated crash reduction from 7.3% to 21.7%. The California component indicated crash reductions of 7.3%. This study also indicated an overall reduction of about 14%.

The 1997 New York State Thruway study indicated a 65% to 70% reduction. However, in a 1999 New York Times article regarding the New York State Thruway study, an official stated: "The experiment is not pure, however, because Troop T has also been conducting a campaign to reduce drunken driving and increase seat-belt use, both of which would also reduce the number of fatal vehicle accidents" and "From 10 to 24 percent of crashes are estimated to involve fatigue or inattention of some kind, but these numbers are based on guesswork."

Despite this, the New York State Thruway study indicating a 65% to 70% reduction continues to be cited in literature.

New Zealand used rumble strips in small applications since the late 1980s, and started a larger program in 2004. Research in the country indicated that lane delineation with rumble strips reduced crashes by an average of 27% over all crash types and studies, with types of crashes such as "run off road" being reduced by up to 80% in some studies. Centre-line rumble strips showed similar effects. However, it appears that there were other crash reduction initiatives that may have contributed to the relatively sizable results.

The effects remained even after road users had become accustomed to the feature, while other road safety measures (when studied at specific installations) often showed declining effectiveness over time. Cost-benefit analysis showed that even on relatively low-volume roads, the costs of applying the markings were quickly exceeded several-fold by the economic benefits of improved road safety (as counted by the reduction of accident rates weighted against the average social costs of a crash).

Further research in New Zealand led to recommendations that strip edge lines and centre lines be marked over extended lengths of road, rather than just at focal points and accident black spots. Apart from the safety benefits of providing a consistent road environment, continuous markings provide valuable alerts to drivers long before the more common accident spots.