Interstate 15 construction through Utah County has never been described as cheap, but numbers shown to legislators Monday indicate it could reach an eye-popping $7 billion.

"There's a great deal of sensitivity to these assumptions," said Carlos Braceras, deputy director of the Utah Department of Transportation. "Inflation on a project this size runs about $400,000 a day."

"Are you going to bring us some bids today?" quipped Rep. Wayne Harper, R-West Jordan.

Inflation includes rising construction costs, which have gone up double-digits in recent years because of construction booms in developing countries such as China.

The I-15 project aims to add two lanes in each direction from south Salt Lake County through Payson, but that's not all.

The freeway needs complete replacement, so it won't be as simple as slapping on a few extra lanes.

"We've really maxed out what we can to with our interchanges and those bridges," Braceras said.

Even with strategic roadways being widened in advance to hold additional traffic, it's going to be slow going for drivers.

The $7 billion price tag includes $5 billion in construction costs and another $2 billion in interest on bonds.

The project, with a completion date of 2016, is at the top of UDOT's list. Funding is being pushed by Utah County's lawmakers who, along with the rest of the county, had to watch Salt Lake County suck up most of the transportation dollars for years in preparation for the Olympics.

How much funding and how quickly the state should provide it were also brought into question Monday. While the state could save several hundred million by putting all its resources into I-15 in Utah County, that would leave nothing for other high-profile projects like the Mountain View corridor.

Interstate 15 through Utah County:

• 43 miles

• 19 reconstructed interchanges

• 2 new interchanges

• 2 new lanes in each direction

• Frontage roads

• Projected start/completion: 2009/2016