DALLAS (CBSDFW.COM) – Drivers cannot help but notice what is going up alongside of Interstate-35E, south of LBJ Freeway. The construction has kept drivers like Ulysses Diaz Deleon guessing. “I guess a double-decker kind of bridge or something?” he asked.

“You know, I’ve been watching them put those up and I can’t figure out what it is,” said Marilyn Magnin, another driver. “I thought it was going to be the elevated train lines, then I started thinking — nope, it looks more like a road.”

She’s right. It is a road. And even though it is along Interstate-35E, it is all part of the LBJ Freeway expansion project.

Crews are building elevated express lanes on both sides of Interstate-35E. They stretch about three-and-a-half miles, from Loop 12 to Valwood Parkway, just north of the LBJ Freeway. The two lanes will be anywhere from 16 to 30 feet in the air, and will take drivers directly to and from Interstate-635.

“It’s going to be a unique feature that people are going to have to get accustomed to drive and understand where it goes and what it does,” said Andy Rittler of the LBJ Express Project.

The elevated express lanes will be tolled, just like new lanes being built on the LBJ Freeway itself. There will also be a guarantee that traffic will flow at least 50 mph. If not, toll rates will increase until traffic is back up to speed. “What that does is allow drivers to make the market choice whether or not they want to continue to pay the toll and that price, or get off those lanes and take a different option,” said Rittler.

But will drivers be willing to pay more for access on the tolled express lanes?

“I drive the tolls all the time,” DeLeon said. “If it’s a benefit, great. But sometimes I avoid it because it gets expensive.”

“Yes, I would, because it gets backed up and I would get home faster,” Magnin said.

Construction on the LBJ Express Project is expected to be complete by December 2015. Toll rates have not been set yet.

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