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Austin's I-35 plans revised to include new cap and a $25 million boardwalk

An aerial view of I-35 through downtown Austin. The sky is blue and several downtown high rises are under construction. This photo was taken mid-day, so traffic volumes are moderate.
Nathan Bernier
TxDOT is planning to start construction on the I-35 expansion in Central Austin early next year.

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The I-35 expansion through Central Austin is undergoing significant revisions as local officials try to negotiate improvements to the $4.5 billion project, aimed at widening the highway that's cut through downtown Austin since it opened in 1962.

Adjustments to the once-in-a-generation project include the possibility of covering larger sections of the highway north of downtown, constructing a $25 million boardwalk on Lady Bird Lake and filtering stormwater runoff into the Colorado River.

These details were outlined in a July 19 letter from Mayor Kirk Watson to advocates fighting to limit or halt the highway expansion. When Watson was a state senator, he played a big role in securing money for the I-35 project.

A trio of Austin City Council members this week posted Watson's letter online — revealing to the public these latest changes — and voiced their concerns about the I-35 expansion while suggesting improvements to pedestrian safety, air quality and stormwater filtration.

Construction on the I-35 Capital Express Central project is slated to begin early next year and take eight years to finish. The Texas Department of Transportation intends to add two "managed lanes" — for vehicles carrying two or more passengers — from Ben White Boulevard to U.S. 290 East. The upper decks north of downtown, built in 1975, are set to be demolished, and bridges crossing the interstate will be rebuilt and made wider to include more space for pedestrians.

TxDOT's transformation plans include lowering the main lanes for much of the distance between Oltorf Street and Airport Boulevard. The City of Austin hopes to cover these lowered portions of the highway with "caps" — basically large decks — that could support buildings at least two stories tall. TxDOT won't pay for the caps, but will engineer the highway to allow for their installation.

After demands from Cherrywood residents, TxDOT agreed to lower the highway deeper north of downtown to allow for another cap, either from 32nd Street to 38 1/2 Street or from 38 1/2 Street to Airport Boulevard.

A schematic showing the two cap options
This illustration shows two proposed caps over I-35, shaded in green. One would stretch from 32nd Street to 38 1/2 Street. The other option would install a cap from 38 1/2 Street to Airport Boulevard.

The president of the Cherrywood Neighborhood Association said he was glad to learn about the possibility of a new cap. But he was reluctant to state a preference for one over the other.

"I don't want to come across like we're looking a gift horse in the mouth here, because we are getting something that we've been calling for," Jim Walker said. "I don't want to get caught in an either-or trap. I think there are some other design changes and refinements that could be made to allow for an even better iteration of a cap in that area."

TxDOT insists there can't be a cap over the entire stretch from 32nd Street to Airport Boulevard, because EMS vehicles need ramps to access St. David's Medical Center at 32nd Street.

The city is still searching for ways to pay for the caps, last estimated to cost up to $800 million. Adding a cap from 38 1/2 Street to Airport Boulevard could increase the price tag by roughly $200 million. That doesn't include millions of dollars for maintenance and operations each year.

A TxDOT illustration showing caps over I-35 in downtown Austin. The northbound and southbound frontage roads under this proposal would be configured to run side-by-side as a boulevard-style thoroughfare.
A TxDOT illustration shows caps over I-35 in downtown Austin. The northbound and southbound frontage roads under this proposal would be configured to run side-by-side as a boulevard-style thoroughfare.

Lowering the highway creates a new demand for drainage in a city prone to flash floods. TxDOT is set to construct a near half-billion-dollar drainage system, which includes a tunnel under Cesar Chavez Street that would direct stormwater runoff into the Colorado River near U.S. 183.

Austin's Watershed Protection Department has been working with TxDOT to develop a stormwater treatment system that meets "City of Austin standards for water quality," Susan Garnett, a spokesperson for the department, said. The current design would not have the capacity to treat all stormwater runoff, she said. TxDOT says the system would include debris screening and sediment removal.

TxDOT also has plans to build a $25 million boardwalk along Lady Bird Lake between South First Street and South Congress Avenue. The project is proposed as a replacement for the loss of other parkland protected by federal law. The Trail Conservancy has been working on the project for months with TxDOT and Austin's Parks and Recreation Department.

An aerial view of the south shore of Lady Bird Lake between the South Congress and South First Street bridges. The Hyatt Regency Hotel rests between them. A large patch of what looks like seaweed or green sludge is in Lady Bird Lake. Much of this is fanwort or cabomba. Read more about that at
Nathan Bernier
TxDOT would build the $25 million boardwalk on the south shore of Lady Bird Lake in front of the Hyatt Regency Hotel.

The state agency has offered to give Austin the Texas Dental Association building on the I-35 frontage road in South Austin near Mariposa Drive. Watson says the city could use the building for whatever it wants, but on-site parking would be reduced as TxDOT expropriates land for the highway. The building and land was appraised by Travis County at around $3.5 million.

In his letter, Watson notes that TxDOT has agreed to post speed limits of 35 miles per hour along I-35 frontage roads downtown. The Austin City Council voted in February to ask TxDOT to keep speed limits on frontage roads no higher than those on nearby streets.

According to Watson, TxDOT has agreed to build a direct connection to I-35 for buses at Capital Metro's Tech Ridge Park and Ride, build noise barriers around a community garden and add boxes for bats under the new I-35 bridge over Lady Bird Lake.

The three Austin City Council members who published Watson's July 19 letter — Zo Qadri, Chito Vela and Ryan Alter — said they're pleased to see "significant improvement in the designs," but they also raised substantial concerns.

Key issues include pedestrian and cyclist safety at intersections, particularly the new interchanges planned at Riverside Drive and Airport Boulevard. The council members have called for more pedestrian and bicycle crossings between Airport Boulevard and 41st Street and between Riverside Drive and Ben White Boulevard.

Traffic on I-35
Gabriel C. Pérez
The highway expansion includes adding two HOV lanes in each direction from Ben White Boulevard to U.S. 290 East.

They also propose capturing and treating vehicle emissions under the caps, provided the city finds the money for their construction.

"Our kids, our grandkids, our great grandkids, our decisions now are the things that are going to affect their lives," Qadri said. "We can either be the City Council that does right, or we can be the City Council that leads to devastation and hurt and pain going down the road."

Details of the changes to the I-35 project surprised advocates who have spent years trying to reduce the potential impact of the highway expansion. They had attempted to enlist state lawmakers to press their case with TxDOT. Then they received the letter from Watson — after he had met with the same delegation of Democratic legislators — outlining the latest developments.

"There's no opportunity for TxDOT to show their work and say, 'Hey, these are the things we've done,'" said Heyden Black Walker with Reconnect Austin, a group that has pushed to bury I-35 through the urban core. "They continue to make changes, and a lot of those changes are positive, but nobody knows what they are."

Another advocate who received Watson's letter said TxDOT often tries to sweeten the deal with local officials near the end of a highway project's planning stages.

"This is not the first freeway project that I've opposed or tried to make better," Jay Blazek Crossley, executive director of the nonprofit Farm and City, said. "We are in the period where TxDOT's trying to seal this deal."

Rethink35, a group striving to remove the highway through Austin and replace it with an urban boulevard, was least impressed with the mitigation measures.

"Some of the things there are very silly, like bat boxes under the bridge. Those were obviously not the kind of changes that people were looking to make," Miriam Schoenfield with Rethink35 said. She said other TxDOT changes were an improvement over the status quo but "nowhere close to sufficient."

Nathan Bernier is the transportation reporter at KUT. He covers the big projects that are reshaping how we get around Austin, like the I-35 overhaul, the airport's rapid growth and the multibillion dollar transit expansion Project Connect. He also focuses on the daily changes that affect how we walk, bike and drive around the city. Got a tip? Email him at Follow him on Twitter @KUTnathan.
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