Truck drivers and car drivers, along with anyone in between, will soon be able to legally drive up to 80 mph on 488 miles of rural interstate highway in Wyoming.

On July 1, Wyoming Department of Transportation crews will begin the process of changing speed limit signs along three sections of Interstate 25, totaling 268 miles in length, as well as on three sections of I-80, for 116 miles, and two sections of I-90, for 104 miles.

The agency hopes to complete sign changeover work by the beginning of the Fourth of July holiday weekend.

Drivers should be aware that during the transition, the 75 mph speed limit will remain in force until the new 80 mph signs are in place.

In approving the speed limit increase earlier this year, state legislators directed the state DOT to conduct a study of the three rural interstate routes to determine where a speed limit of 80 would be appropriate.

Factors considered in the study were roadway characteristics, including curves, grades, width and proximity of interchanges, as well as traffic patterns, including current average speeds, traffic volumes and proportion of commercial trucks and passenger vehicles. Also considered were safety statistics, including crash rates and relative severity of crashes in terms of numbers of fatalities and serious injuries.

Road sections where the 80 mph speed limit will be implemented are:


  • North of Cheyenne to south of Douglas; 117 miles, mileposts 18-135;
  • North of Douglas to south of Casper; 44 miles, mileposts 141-185; and
  • North of Casper to south of Buffalo; 107 miles, mileposts 190-297.


  • East end of Bridger Valley to west of Green River; 34 miles, mileposts 48-82;
  • East of Rock Springs to west of Wamsutter; 55 miles, mileposts 110-165; and
  • East of Cheyenne to west of Pine Bluffs; 27 miles, mileposts 373-400.


  •  East of Buffalo to west of Gillette; 64 miles, mileposts 59-123; and
  • East of Gillette to between Moorcroft and Sundance; 40 miles, mileposts 130-170.

The state DOT is continuing to assess two other sections of interstate where a speed limit increase could be possible. One section, measuring 46 miles, is I-80 from west of Rawlins to just west of Walcott Junction. The other section, measuring 17 miles, is I-90 from east of Sundance to the South Dakota state line. WYDOT does not have a time frame for completing the additional study.

It said it will continue to monitor those Interstate sections going to the 80 mph speed limit this summer. The results of the speed limit increase will be revisited to determine if further changes in section lengths will be warranted.

Wyoming now joins Utah and Texas as states which have speed limits above 75 mph on select rural highways. Idaho is also preparing to implement an 80 mph speed limit on some of its Interstate highways, but trucks will be limited to 70 mph.