Amish claimed that the shoulder rumble strips were dangerous for horse-drawn carriages, and successfully lobbied to have them paved over. In 2010, Kansas has considered removing shoulder rumble strips from an interstate highway to allow buses to travel on the shoulder during periods of traffic congestion. Accident and driver dynamics On-road and run-off-road accidents Single-vehicle crashes are classified into two groups: run-off-road (ROR), and on-road (OR) crashes in which the vehicle remains on the road after the crash. ROR crashes can account for up to 70% of the fatal single-vehicle crashes. ROR crashes are due to inattention, speeding, traction loss, overreaction, crash avoidance, and mechanical failure. Rumble strips only prevent ROR crashes due to inattention. Research indicates that 47% of RORs exited the highway to the left; while 53% exited the highway to the right (in the USA where driving is on the right-hand-side of the road). Inattentive driving A US Federal Highway Administration (FHWA) sponsored study stated that driver inattention comes in many forms, including distraction, daydreaming/competing thoughts, fatigue/drowsiness, and alcohol/drug impairment. Early evening low alcohol intake also worsens sleepiness-related driving impairment. In a 2008 survey in the US, 33% of fatally injured drivers tested were found to be legally impaired (BAC > 80 mg %), and an additional 5% were found to have a legal amount of alcohol in their bodies. Canada has similar statistics. Migration of accidents Studies support the hypothesis that some crashes are not prevented, but merely "migrated" or displaced from vehicle to vehicle, season to season, or location to location (e.g., further downstream of rumble strips on the highway system), and that such crashes may be no less severe than ones prevented by rumble strips. An FHWA sponsored study wrestled with the moral dilemma of rumble strips keeping "unsafe drivers" (which includes impaired drivers) on the highway. "This group of unsafe drivers temporarily saved by the rumble strips may have caused some multiple-vehicle crashes involving harm to innocent victims to occur downstream from the treated site where no rumble strips existed. Unfortunately, as noted above, an examination of downstream crashes could not be conducted." A 2008 Swedish study using a driving simulator and 35 sleep-deprived drivers concluded: "The main results showed an increase in sleepiness indicators from start to before hitting the rumble strip, an alerting effect in most parameters after hitting the strip. The alertness enhancing effect was, however, short and the sleepiness