Transportation

I-35 tunnel vision: Austin nabs $105 million for highway caps

KUT 90.5 | By Nathan Bernier

Published March 12, 2024 at 11:50 AM CDT

An aerial view of I-35 in downtown Austin. Traffic volumes are moderate. It's a sunny day. Buildings line the highway. — The main lanes of I-35 will be lowered 30 to 40 feet through downtown as the highway's footprint is widened. The City of Austin wants to cover the lowered highway with caps that cost hundreds of millions of dollars, but TxDOT won't pay for it.

Austin is getting closer to raising the money it needs to put I-35 in a partial tunnel after Texas lowers the main lanes 30 to 40 feet from Holly Street to Airport Boulevard. The city just raked in a $105 million grant from the U.S Department of Transportation, and the council could vote next week to borrow $193 million more from a state infrastructure bank.

The Texas Department of Transportation is planning to sink the lanes as part of a decade-long construction project that includes tearing down the upper decks and adding four high-occupancy vehicle lanes along an 8-mile stretch from Ben White Boulevard to U.S. 290 East.

TxDOT won't pay to cover the lowered lanes, but will install so-called caps over the trenched highway if the City of Austin and University of Texas foot the bill. The city could also add mini-caps, so-called stitches, that stick out of bridges to create more public space.

A high-level view showing possible caps covering Cesar Chavez to 7th Street. Another cap would be installed between 11th and 12th Streets. UT-Austin is considering covering the highway from 15th Street to Dean Keeton. A smaller stitch is possible at 32nd Street. And the last cap would stretch from 38 1/2 Street to Airport Boulevard. — Under the most expensive plan, I-35 would be covered from Cesar Chavez to Seventh Street, from 11th to 12th Streets, from 15th Street to Dean Keeton and from 38 1/2 Street to Airport Boulevard. UT would pay for the 15th Street to Dean Keeton caps. Smaller decks called "stitches", which don't require fire suppression and ventilation equipment, could be built at Holly, 32nd and 51st streets.

Austin is considering spending $881 million or more on a menu of caps and stitches that would create slightly more than 27 acres of space. Caps would cover the highway from Cesar Chavez to Seventh Street, from 11th to 12th and from 38 1/2 Street to Airport Boulevard. Stitches would be installed at Holly Street, 32nd Street and 51st Street.

A rendering showing a cap over I-35 covering Cesar Chavez. The pasted in images of people appear to be oddly placed and mismatched in size. — The City of Austin included this rendering, intended to show a cap over I-35 at Cesar Chavez, in the press release announcing it won a $105.2 million grant from the U.S. Department of Transportation.

Annual operations and maintenance would cost up to $35 million, according to a staff estimate. Caps require large and costly ventilation and fire suppression systems. For comparison, Austin spends almost $40 million per year on municipal courts.

Meanwhile, the city wants to borrow up to $193 million from a special loan fund managed by TxDOT. The State Infrastructure Bank provides low-interest loans for transportation projects. The City Council is scheduled to vote on whether to apply for the loan at a March 21 meeting.

Even with the TxDOT loan, the city would still be hundreds of millions of dollars short from being able to pay for caps and various amenities on top. Some caps could be constructed to support buildings. Other ideas for amenities have included parks or elevated walkways.

A rendering showing buildings and parks where I-35 would be. — One vision of what could go on caps over I-35 included multistory buildings and public park space. This was the lead image on a consultant's report about the cost of caps.

Other options under consideration to pay for construction include selling naming rights to a cap or a stitch. A bond election, asking voters to fund the caps with property tax revenue, is also on the table.

Austin already paid TxDOT $15 million late last year to start designing the caps and stitches. Another $19 million is due by December to finish the blueprints. The city could have to start paying for construction of the caps as soon as 2026.