Idaho, Wyoming to Hike Speed Limit to 80mph They join Texas, Utah with highest limit By Rob Quinn, Newser Staff Posted Mar 27, 2014 1:12 AM CDT 49 comments Comments A worker installs a highway sign in Utah after the speed limit was raised. (AP Photo/Utah Department of Transportation) (Newser) – Idaho and Wyoming are set to join Texas and Utah as America's fastest states, with speed limits on certain highways boosted to 80 miles per hour. Lawmakers in both states have approved the rise, with advocates noting that a similar law in neighboring Utah did not contribute to a rise in accident rates, apparently because most drivers were already doing 80mph before the law came in, Fox reports. The Idaho Department of Transportation—which opposed raising the limit—will determine which highways can safely handle an increase in speed. "We are trying to decide what the locations will be the speed limit increases. How are we going to factor in weather conditions and concerns?" a spokesman for the department tells KMVT.