based on Interstate (freeway, turnpikes, thruways) test sites have minimum paved shoulders and very high crash rates due to inattention. The collision reduction attributed to the installation of CSRS is mainly a function of stable shoulder width, crash rate and profile, climate and diminishing marginal returns. Centerline rumble strips (CRS) Centerline Rumble Strips are applied to single-lane undivided highways to help prevent head-on collisions. When present, these are often milled into the pavement. A 2005 National Cooperative Highway Research Program (NCHRP) study concluded that overall motor vehicle crashes at sites treated with Centerline Rumble Strips were reduced overall by 14%. In these situations the opposite lane and any paved shoulder would function as a generous recovery zone. However, this study did not investigate changes in crash severity, as did the 2005 Montana study. It is interesting that the CRS reduction value is the same as the 2005 Montana CSRS study that indicated a 14% reduction in accidents on Interstate highways. This supports the hypothesis that the overall effectiveness of CSRS with a generous recovery zone is about 14%. Ice and slush filled rumble strips can be a concern, particularly so for milled centerline rumble strips. For this reason, some jurisdictions are reluctant to install them. A 2015 Federal Highway Administration study evaluated the application of shoulder rumble strips and centerline rumble strips in combination by analyzing geometric, traffic, and crash data obtained at treated two-lane rural road locations in Kentucky, Missouri and Pennsylvania. The results suggested that the effect of combining centerline and shoulder rumble strips further reduces run-off-road crashes compared to shoulder rumble strips alone and both total and fatal+injury crashes compared to centerline rumble strips alone. However, it appeared that shoulder rumble strips do not further reduce head-on+sideswipe-opposite-direction crashes than applying centerline rumble strips in isolation. Continuous lane rumble strips (CLRS) CLRS are applied to multiple lane highways to help prevent vehicles from drifting into the adjacent lane and possibility colliding with an overtaking vehicle. These are typically a raised reflective system. Transverse rumble strips Transverse rumble strips (TRS) may be used to warn drivers: of the need to stop (e.g. intersections, toll plazas); the need to slow down; the need to change lanes; of a change in roadway alignment; that they are leaving the traveled way; upcoming construction zones; wildlife crossings; and other potentially unexpected conditions. As a speed reduction measure, TRS have been marginally successful. A