BELOIT — Officials unveiled Thursday one of the most expensive highway projects in state history, but it is designed to do more than ease congestion.

The $715 million reconstruction and expansion of a 45-mile stretch of Interstate 39-90 between Madison and the Illinois state line will aid state tourism and help create more economic development along the corridor, one of the busiest stretches of highway in the state, officials say.

The eight-year project is scheduled to begin in 2015, but construction of the Highway 11 interchange in Janesville is scheduled for 2013.

"This is a really great day for Wisconsin," said state Transportation Secretary Mark Gottlieb. "This represents a $715 million vote of confidence for Wisconsin. It's a vote of confidence in our economy and a vote of confidence in the importance of transportation infrastructure."

The project will replace pavement, add a third lane in each direction, replace two bridges over the Rock River and replace nearly 100 other smaller bridges on the route.

Unlike most major highway projects where the federal government can cover 80 to 90 percent of the work, the I-39-90 project will be 70 percent state funded and 30 percent federal, said John Vesperman, the Department of Transportation's project chief.