Speed limit now 80 mph from Sundance to South Dakota

August 20, 2015

An 80 mph speed limit is now in effect on a 17-mile section of Interstate 90 in northeast Wyoming.

The increase affects I-90 between the East Sundance Interchange (milepost 190)  and the South Dakota border (milepost 207).

Motorists should note that a 75 mph speed limit remains in place on an adjoining 20-mile stretch of I-90 (mileposts 170-190) between Sundance and Inyan Kara, about 15 miles east of Moorcroft.

Other sections of I-90 already posted at 80 mph include 64 miles between Buffalo and Gillette and 40 miles between Gillette and Inyan Kara.  The 80 mph speed limit is in also in effect on 268 miles of I-25 and 116 miles of I-80.

The initial speed limit increase to 80 mph occurred in July 2014, after the Wyoming Legislature directed WYDOT to conduct a study of 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.

At the time of the original study, the Sundance-South Dakota section of I-90 was affected by road improvement work, so WYDOT opted to wait for the work to be completed before undertaking the additional study that resulted in the latest speed limit increase.

The 505 miles of interstate highway in Wyoming on which the 80 mph limit is in effect are:


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);
East of Cheyenne to west of Pine Bluffs; 27 miles (mileposts 373-400).


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 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)
East of Sundance to the South Dakota border; 17 miles (mileposts 190-207)