Utah, which has allowed 80-mph travel on some stretches of interstate highway since 2008, has been studying the effects of the increase for several years and has found that its drivers are involved in fewer accidents and are more likely to comply with posted speed limits than they were prior to the limit hikes.
According to Missoulian.com, studies conducted in 2012 showed 11-20% decreases in speed-related crashes along sampled sections of Interstate 15 in Utah. A 2009 study found that the number of drivers exceeding the posted limit decreased by 20% when the limit was raised. 36% of Interstates in Utah currently are currently 80 mph.
Wyoming and Idaho recently joined Utah in raising speed limits on some rural interstates to 80 mph. As the limits were raised earlier this year, neither state has sufficient data to make any conclusions about possible safety impacts, however Boise Weekly reports that the Idaho State Police have handed out more citations during the period from July (when the limit was raised) to November of this year than they did in 2013.
Lawmakers in Montana are looking to join their neighbors in raising limits, and bills expected to be introduced by state legislators next year could make that a reality.