DALLAS — Transportation officials are considering funding options for a $4.4 billion expansion of Interstate 35E between Dallas and Denton that could be the largest of several major projects in the area.

With only $450 million currently available, officials are drawing plans for toll lanes on which the fees would increase with congestion.

If Texas and local governments decide to go with public-private partnerships to build the project, bonds could be issued by a consortium similar to those rebuilding two other freeways in the area.

The $4 billion LBJ Freeway/Interstate 635 project north of Dallas and the $2 billion North Tarrant Express in Tarrant County could serve as models for I-35E with bonds backed by tax revenues and investment from private equity.

To prepare for construction on I-35E, the Texas Department of Transportation has already begun the process of buying the nearly 200 private properties along the expansion route. After relocation of utilities, construction on the 12-mile central segment of the I-35E project could begin by 2013, according to Gary Bailey, Denton-area engineer for TxDOT.

To use those funding templates from the LBJ Freeway and North Tarrant Express, the state would need authorization from the Legislature, which begins meeting in January.

Under existing law, private developers such as the Spanish firm Cintra are not allowed to start any new public-private projects. The LBJ Freeway and North Tarrant Express were allowed to proceed under 2007 legislation because they were already in the planning stages when the Legislature declared a moratorium on new projects.

In the same session, lawmakers stripped Cintra of the $3.5 billion State Highway 121 project that it had been awarded. The project was then handed over to the North Texas Tollway Authority after a bidding process.

One funding mechanism TxDOT is considering for I-35E is pass-through tolling, in which a local government or private developer fronts the money to build a project. TxDOT then pays the developer either a set amount based on the “availability” of the road when it opens or on a per-car toll basis, regardless of whether the highway is tolled. The developer is guaranteed a set reimbursement.

The project would widen I-35E from the current six lanes to 12. The total length of the project would be 28 miles.

The new freeway would be one of two major projects to ease traffic between Dallas and Denton, a college town that sits atop a triangle between Dallas and Fort Worth.

Interstate 35, which splits between eastern and western segments in the town of Hillsboro to the south, merges again into one highway in Denton.

I-35 from Hillsboro to Bell County, north of Austin, is also undergoing expansion.

In addition to the freeway expansion, Denton County is building a $200 million rail line to the north Dallas suburb of Carrollton, where it will link with Dallas Area Rapid Transit’s new Green Line.

The Green Line is scheduled to open Dec. 6, while the Denton County “A-Line” is expected to begin service June 30.

Money for the rail line has come primarily from a $3.2 billion payment the NTTA made to the region for the right to build the SH 121 tollway, under construction as the Sam Rayburn Tollway.

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