Topeka ? This is the big one.

Kansas Turnpike Authority officials on Tuesday unveiled plans to replace the double bridge over the Kansas River in Lawrence at a cost of about $140 million.

The project will mean higher tolls and traffic problems, but Michael Johnston, president and chief executive officer of the KTA, said the finished product will make it worth the cost and hassle.

“This project will be a challenge during construction, but when it’s finished it will better serve our customers and improve access between East and West Lawrence” interchanges, Johnston said.

He said engineering consultants have told the authority that the current bridges have reached the end of their life expectancy of 50 years and need to be replaced by 2012.

The $140 million estimated price tag makes the bridge project the most expensive one on the Kansas Turnpike, and is approximately what it cost to build the entire 236-mile road in the 1950s.

Construction is scheduled to start in May 2008 and be completed in about three years, by fall 2011.

Once finished, the project will have two new 2,300-foot bridges, which will have three lanes each and 10-foot wide shoulders; realigned approach ramps and acceleration lanes to and from the East and West Lawrence toll plazas; and an additional entry and exit lane at Plaza 204, known as the East Lawrence interchange.

The dirt will start flying within days.

“There is stuff going on now that is just prep for this project,” said Rex Fleming, the project’s chief engineer with the authority.

On Tuesday, the bridge that carries North Michigan Street over the Kansas Turnpike at milepost 202.2 will close for six to eight months for reconstruction. When the Michigan Street project is complete, the North Iowa Street bridge will close for similar reasons, also for six to eight months.

Starting in May 2008, there will be no westbound access to and from Plaza 202 at the West Lawrence interchange for eight months. After that is finished, the East Lawrence interchange will be closed for eight months. Improvements are planned at both plazas.

Fleming also said an additional lane being built at the Lecompton toll plaza will help traffic flow during work on the Lawrence plazas.

Tolls on the turnpike are increasing an average of 5 percent starting July 1. Part of the increased tolls are going toward paying for the bridge and plaza project, Johnston said.

In announcing plans for the project, turnpike officials also closed the book on the widening project between Lecompton and Topeka that added a lane in each direction for 12 miles.

Johnston said that project, which started in 2003, cost $65 million and was done on time. He said it was a discretionary project “done only to provide better service to our customers.”