The Legislature approved the new, faster zones during the last session. State Department of Transportation workers are putting up the new signs this week, said spokesman John Gleason.
The change was spurred by a Department of Transportation study based on three years of data from experimental stretches of Utah highways with 80 mph speed limits. The evaluation concluded that fewer crashes occurred because drivers were traveling at similar speeds, decreasing the danger when lead-footers come up on slower drivers.
The new, permanent fast zones include Interstate 80 from the Nevada border to Utah Route 36 in eastern Utah, and Interstate 15 from north of Brigham City to the Idaho border in northern Utah.
Speeds will also be increased on I-15 between Santaquin and North Leeds in central-southern Utah. The 75 mph zones remain on that stretch through two mountain passes and Cedar City.
"As soon as the signs are posted, they are official," Gleason said.
None of the 80 mph zones are within the heavily populated Wasatch Front, a string of cities from Brigham City on the north to Santaquin on the south that is home to nearly two-thirds of Utah's 2.8 million residents.
Texas also has roads with speed limits surpassing 75 mph, including a toll road with a speed limit of 85 mph.
Before passing the legislation, the sponsor, Rep. James Dunnigan, R-Taylorsville, made sure Utah wouldn't lose federal funding after staking its 80 mph signs.