Since Utah has bumped up the Speed Limit to 80 mph on some rural interstate highways, It has experienced an overwhelming amount of speeding. The Insurance Institute of Highway Safety (IIHS) estimates that vehicles are 120% more likely to exceed this speed in these zones. The IIHS found that the average speed was ± 3 mph of the 80 mph mark. An increase from 75 to 78 mph increases the chances of a fatal crash by an estimated 17%. 6 states have adopted 80 mph in some interstate stretches, but the minutes you may shave off driving are not worth the risk of death, by driving that fast.