[Myrddin]

Most of the I-15 north of Las Vegas to Provo, UT is 75 MPH. There is a 55 MPH through the Virgin River Gorge, 65 MPH through St. George and about 4 stretches of 20 miles each at 80 MPH. Provo to Ogden slows to 65 MPH, then back to 75 MPH from about UT-I-15-MP-349 to Pocatello, ID.

[colorcountry]

There are a few test strips North of Filmore and one North of Scipio that are 80 miles per hour....and it seems to be working well.

[Vigilanteman]

There is a 55 MPH through the Virgin River Gorge . . .

One of the most spectacular and beautiful stretches of highway in the nation. You would have to be a suicide jockey to take it at much more than 55 mph.

Interesting fact: I-15 through Utah and I-80 through Wyoming are both close to exactly 400 miles long. The last mile mark going north or east on either is, if I recall, either 400 or 401.