The Texas Department of Transportation is proposing to depress the I-35 lanes from 15th Street to Cesar Chavez Street as a way to improve mobility.[/caption]

In the next 10 years drivers on I-35 could find congestion relief from a $4.3 billion plan the Texas Department of Transportation has underway.

That relief could come from the addition of an auxiliary lane—meaning it is not continuous throughout I-35—on the upper decks of I-35 between Airport to Martin Luther King Jr. boulevards as well as depressing the I-35 main lanes from 15th Street to Cesar Chavez Street. TxDOT additionally is proposing to extend a fourth main lane south of 12th Street to Cesar Chavez.

The proposals are part of TxDOT’s Mobility 35 plan in Hays, Travis and Williamson counties. The Downtown Stakeholder Working Group comprising neighborhood groups, I-35 users and government entities provided input on projects.

“I believe this is the first time the region has had a 10-year plan for Interstate 35 projects,” Sen. Kirk Watson, D-Austin, said at a June 15 Greater Austin Chamber of Commerce event. “For the first time we have a good idea of what we need to do and when we need to do it.”

Adding the auxiliary lane and retrofitting support beams to handle additional weight would occur at the same time as construction of the Future Transportation Corridor, which will be a pair of express lanes extending throughout the I-35 corridor in Central Texas.

“The [traffic] models show that adding these auxiliary lanes will double the travel speed on those decks during peak times,” Watson said.

The catch is the $4.3 billion plan is underfunded, Watson said. Four I-35 projects in the region will be under construction within one year because of funding from Proposition 1, which voters approved in November to divert a portion of the oil and gas tax revenues toward the State Highway Fund.

“The funding puzzle is not completely solved … ,” Watson said. “One of the things I’ve been pushing hard is [to] get this 10-year plan in place so that we’re ready any time money is available.”

TxDOT has repeatedly said it is about $5 billion short annually needed to maintain the existing state highway system. Watson said Prop. 1 helps bridge that gap as well as ending the practice of diverting gas tax revenues from transportation, which is estimated to bring in another $600 million annually.

More TxDOT funding could become available if voters approve a constitutional amendment in November. This amendment would divert toward the SHF $2.5 billion from the state’s sales and use taxes after revenues exceed $28 and 35 percent of growth from the motor vehicle sales tax after state revenues exceed $5 billion.

“As we start what is a very good step, I think it’s clear we’re not done,” Watson said. “… We have to find new and dependable sources for transportation.”

Austin Mayor Steve Adler said the city supports TxDOT depressing the I-35 lanes with the ability for the community to cap those lanes in the future. He said TxDOT would not fund the caps because they would not contribute to mobility.

“This vision is going to take local championship and local funding,” he said.