"For the most part, people drive what they consider to be a comfortable, safe speed for the road they're on, considering the traffic and the weather conditions."
A 2009 Utah study on stretches of Interstate 15 in that state found drivers complied better with an 80 mph speed limit than with the previous 75 mph limit. The study showed a 20% reduction in drivers exceeding 80 mph.
Data from a separate 2012 study of two portions of I-15 in Utah found an 11% to 20% drop in speed-related crashes, depending on which stretches were studied.
Montana also has a pending bill to raise to 80 mph - possibly 85. So far, four states have speed limits at 80 mph or above: Idaho, Wyoming, Utah, and Texas. Nevada even had a bill this year to raise their speed limit to 85 mph, but their DOT had its head up their ass and one of their board members said "Even studying this sends the wrong message that we support increasing the speed limit."
Check out the article on South Dakota below: