As the Texas Department of Transportation tears up Interstate 35 through Austin to expand it, the agency already has its sights set on another segment of the highway a little farther north.
TxDOT wants to widen 13 miles of I-35 in Williamson County between Round Rock and Georgetown, and the department is seeking feedback from the public. Drivers have until Aug. 28 to weigh in.
The project, which would stretch from Texas 29 to Texas 45, is in the preliminary design stages. As currently proposed, it would add two high-occupancy vehicle lanes in each direction through the corridor and one main lane in each direction from Texas 29 to RM 1431. Crews would also relocate entrance ramps and exits, reconstruct bridges and intersections, add bypass lanes and build pedestrian and bicycle infrastructure throughout.
I-35‘s current capacity through the corridor is insufficient to accommodate Williamson County’s explosive growth and projected traffic demand over the next few decades, TxDOT officials said in a recent presentation. In 2025, up to 217,000 vehicles traversed a portion of the project corridor on any given day – a combination of local traffic and long-haul vehicles passing through the region. By 2055, traffic through the area is expected to grow to 380,000 daily vehicles.
Safety is also a factor, TxDOT said. From January 2021 through June 2026, there were 31 deaths and nearly 8,600 crashes – an average of more than four per day – on the highway segment, according to the agency. The number of crashes in the segment is 28% above the state average for urban interstates, TxDOT said.
The proposed improvements could dramatically reduce congestion and travel times, officials said. Without the project, commuters would sit in traffic for up to 36 minutes during the morning rush and up to two hours during the afternoon peak, according to the agency’s modeling. With the expansion, travel times would stay around seven to nine minutes, the modeling shows.
The expansion would also reduce crashes by 20% to 50% by reconfiguring interchanges to reduce potential collision points, TxDOT said.
Heading out to eat mosquitoes, the bats come out from under the Interstate Highway 35 bridge over McNeil Road in 2017.
But the project still faces roadblocks and remains years away from construction. The corridor runs near several environmentally sensitive natural features, including Inner Space Cavern, the Edwards Aquifer recharge zone and a bat habitat.
Inner Space Cavern, located below a portion of the interstate, is home to endangered karst invertebrates, which are tiny animals that only live in caves. The cavern is also a popular tourist stop. TxDOT said it is working with conservationists to study and reduce impacts to the underground ecosystem.
The project would also likely disturb a bat colony that lives under the McNeil Road overpass. TxDOT would have to temporarily displace thousands of bats to demolish the bridge, but the agency said that construction of a new bridge would ultimately provide more roosting space for the colony. The agency would also have to comply with special regulations designed to protect groundwater in the Edwards Aquifer.
TxDOT started studying the project in 2013, and the project entered preliminary design and environmental analysis in 2023. The environmental study is expected to take another two to three years.
Final design and construction could take another eight years combined. TxDOT has not yet identified funding for those phases of the project nor given a timeline for completion.
The public can find additional information and comment on the proposal at txdot.gov, by emailing mobility35@txdot.gov, by leaving a voicemail at 737-345-2971, or by writing to I-35 Georgetown to Round Rock Project, 13620 Briarwick Drive, Suite 100, Austin, TX 78729.
This article originally published at I-35 expansion north of Austin: What TxDOT plans between Round Rock and Georgetown.