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Last year, Utah added 289 extra miles of 80-mph speed limits on selected rural freeway stretches. Now, new legislation could expand the high limits anywhere on the rest of Utah's interstate freeway system wherever studies find that it is safe and makes good engineering sense.

Also, if officials feel speeds should not rise in urban sections all the way to 80, the bill would permit raising them from the current 65 mph to 70 mph or 75 mph instead.

"We're going to look at other pieces of the interstate to see if their posted speed is appropriate," said Rep. Jim Dunnigan, R-Taylorsville, who is drafting the new legislation, and sponsored past bills that allowed 80-mph speed limits along many rural freeways.

Instead of expanding 80-mph zones again piecemeal, Dunnigan said it makes sense now for the Legislature to allow the Utah Department of Transportation to study the entire state freeway system and allow higher limits "as long as there's an engineering basis" to it, and it is in areas with few crashes.

"We're not really breaking new ground. We have now, I think, five years of data from my first test strips" where 80 mph speeds were first allowed on Interstate 15 in southern Utah, Dunnigan said.

State studies found that average speeds in the 80-mph zones have increased by only 1 mph. "Effectively, it's just those who are going to go 80 are now doing so legally. There has not been a big ramp-up of people" exceeding it, Dunnigan said.

"You still have maybe 5 or 10 percent of outliers who will go higher, but for the vast majority — the 80th percentile —  it is 1 mph faster," he said.

Dunnigan said an example of an area where he thinks a new 80-mph limit is very likely to be approved is along I-70 from Green River to the Colorado border. On the other hand, he does not expect congested urban areas to have their speed limits increased, but some might be adjusted a bit.

"There may be some stretches that are 65 that appropriately could be 70, and there may be some that are 75 that could be 80. But I'm not proposing to go higher than 80," Dunnigan said.

Utah allows 65 mph on urban freeways, while 75 is the default on rural freeways — with 80 on select rural stretches that had few accidents, and do not have curves or features that create problems for higher speeds. Texas and Utah are the only states that have speed limits of 80 mph or higher. Texas allows 85 mph on one toll road.

Dunnigan has discussed the bill with UDOT, and received some tentative support.

"If the language comes out similar to what we have seen in the past that allowed us to study the new sections and establish speeds at the appropriate levels based on our engineering studies, then we'll move forward with that," Robert Hull, UDOT director of traffic and safety, said.

Until such studies are performed, Hull said it is difficult to predict where speed limits could increase or stay the same. He said UDOT would first eliminate areas where speed-related crashes have been a problem. Then it would do speed studies and engineering analysis to determine where speed limits could rise safely.

Dunnigan's bill last year to expand 80-mph zones sped through the Legislature with little opposition, although a few raised concerns that it could increase air pollution or make accidents more deadly because of high speeds.

Rolayne Fairclough, spokeswoman for AAA Utah, who had testified against last year's bill and warned it could lead to higher insurance rates, said she would like to see Dunnigan's final bill before commenting on it. "But generally higher speeds are more dangerous," she said.

The bill also comes when reducing air pollution is a hot political topic. Dunnigan notes that UDOT testified last year that newer cars are designed so that they do not create much additional pollution at higher speeds.

"There is some very modest, very minor additional pollution if you go from 75 to 80, but a much bigger determinant is how old is the vehicle because the newer cars just do not pollute much more at a higher speed," Dunnigan said.

Last year, the state extended 80-mph zones into areas including I-80 from Nevada to near Tooele; I-84 from Idaho to near Tremonton; I-15 from Idaho to near Brigham City; and another 116 miles of I-15 in southern Utah generally covering most areas from Santaquin to Leeds (north of St. George).