The federal government has given its blessing to the most expensive road project in Utah history.

The U.S. secretary of Transportation has signed a "record of decision," which is the final approval of the environmental review of Interstate 15 reconstruction through Utah County. State officials are now allowed to begin right-of-way acquisition, design and construction.

"Now we really have a project," said Nile Easton, spokesman for the Utah Department of Transportation. "We're on target for spring of 2010. That's when construction will begin."

For $2.6 billion, the residents of Utah will get several things:

• The project will widen I-15 by two lanes in each direction between American Fork and Spanish Fork, a 50- to 66-percent increase in capacity.

• Many of the interchanges will be rebuilt or reconfigured, as will many bridges. Some of them aren't up to height standards, the result being that they're occasionally clipped by semitrailers.

• Utahns may not know that the project has broader implications. It is part of an 840-mile route connecting San Diego to Salt Lake City that was chosen last year as one of six "Corridors of the Future" by the U.S. Department of Transportation.

But I want it now!

Though construction won't begin until spring of 2010, UDOT has plenty to do. It has to put a request for proposal together as well as straighten out all the right-of-way issues.

"There's actually quite a bit of work to do between now and then," Easton said.

The construction is also expected to take four years, meaning plenty of time to get used to the orange barrels. Easton said UDOT will be using the same design-build process that worked so well on the Salt Lake portion of I-15.

Design-build gives the contractor a little more control and oversight, he said. The trade-off is that projects get done in half the time of traditional methods.

"We still have some oversight, of course. It's not like we wash our hands of the project for four years," he said.