Texas CapEx Central I-35 Expansion

The long-anticipated reconstruction of the downtown segment of Austin’s Interstate 35 (I-35) will do more than alleviate chronic congestion that has long plagued the route – it’s also been designed to bring nearby communities closer together and accommodate additional modes of travel.

As one of the fastest-growing regions in the U.S. for the past several years, improving I-35 is a top priority for the Texas Department of Transportation (TxDOT). The result is TxDOT’s ambitious $4.5 billion, eight-mile I-35 Capital Express Central Project (CapEx Central) between U.S. 290 East and State Highway 71/Ben White Boulevard.

“I-35 is a major conduit for goods and services, running from the southern border ports all the way north to the entire U.S.,” said Stephanie Messerli, PE, AICP, senior vice president and Texas Transportation leader at WSP in the U.S. “As a main artery for the state, it is a very important network for TxDOT.”

CapEx Central will be developed in phases to minimize construction impact on traffic. We designed the complex 1.8-mile critical downtown segment of the I-35 project (CapEx Central-Downtown).

“This highway is considered the third most congested in Texas,” added Arash Saeedi, PE, vice president and local Transportation business leader at WSP in the U.S. “With this project, we’re improving mobility and addressing operational issues and challenges along the corridor, like different ramping intersection improvements, providing better access to and from the highway, and adding auxiliary lanes.”

The I-35 Capital Express Program project represents the first significant upgrade of the I-35 corridor in greater Austin since 1974. It includes three stand-alone projects — North, Central and South — and is part of TxDOT’s wider Mobility35 Program that covers nearly 80 miles of corridor through Williamson, Travis and Hays counties.

Location

Austin, Texas, USA

Client

Texas Department of Transportation

Project Value

$4.5 billion

Project Status

Ongoing, started October 2024

WSP Role

Project Design

Road Length

8 miles

Project Cost

$4.5 billion

Completion Target

2033

img-capex-central-i35-expansion-austin-rendering-1

©TXDOT
Sections of the highway and could feature deck caps that will be transformed into public park and recreation facilities that can be accessed from either side of the highway.

Enhancing Safety and Mobility

CapEx Central Martin Luther King Jr. Boulevard Bridge was the first segment to begin construction, which commenced with a groundbreaking ceremony on Oct. 30, 2024.

CapEx Central includes a specific focus on enhancing safety and mobility throughout the corridor by:

lowering the existing I-35 roadway and adding non-tolled high-occupancy vehicle managed lanes in each direction,
connecting downtown Austin neighborhoods by reconstructing east-west cross-street bridges,
redesigning the CapMetro Red Line crossing at 4th Street to connect to the Austin Convention Center,
adding pedestrian and bicycle paths, and
designing infrastructure support for the “deck caps and stitches” the City of Austin may implement, including deck parks to serve neighboring communities.

“I-35 is not just a major artery—it is used as a local road as well,” Messerli said. “Local motorists are frustrated by trucks using this road and wish they would use SH 130 to bypass downtown Austin. Unfortunately, when you look at the origin and destination of traffic, many of those trucks are making local deliveries, so they have to use I-35 to access downtown. Providing those center lanes is really going to help improve this congestion.”

We are designing traffic control phasing for both the CapEx Downtown and University segments of the highway and are coordinating efforts with various ongoing design and construction projects along the CapEx Corridor.

Plans are designed to maintain traffic flow and minimize impact on I-35 motorists during construction.

TxDOT is targeting project completion for the entire CapEx Central corridor in 2033.

Deck Caps and Stitches

One of the goals of the project is to reconnect neighborhoods that were separated when I-35 expanded into an interstate highway in the 1950s. It became a dividing line between east and west Austin.

One way to reconnect is to lower sections of the highway and “cap” them with a cover that will become an area of public access, providing park and recreation facilities that can be enjoyed from either side of the highway.

TxDOT collaborated with the City of Austin and University of Texas (UT) on the conceptual design of deck caps and stitches along the project corridor. The City of Austin and UT will fund operations and maintenance of these enhancements throughout the life of the project. TxDOT will be responsible for building the infrastructure and implementing fire suppression requirements during construction.

It is a concept that has been used to great success in places like Dallas, where Klyde Warren Park was developed over the Woodall Rodgers Freeway; and Denver’s Central 70 Project, where a four-acre park was built over Interstate 70 and connected two downtown neighborhoods. We were the lead design firm for the Central 70 project.

img-capex-central-i35-expansion-austin-traffic-2

Improvements to I-35 will help improve congestion that has long frustrated motorists traveling through greater Austin.

“The proposal would sync the neighborhoods, similar to what was done at Klyde Warren Park,” Saeedi said. “The idea helps connect the community with parks and amenities on top of the highway.”

The project includes reconstruction of east-west cross-street bridges, adding more than 19 miles of new shared-use pedestrian and bicycle paths, 13 connections to urban trails and bicycle networks, and additional safety and mobility improvements.

“Significantly enhanced pedestrian and bike crossings are key so people can feel safer crossing I-35,” Messerli said. “There’s so much traffic along this corridor, and this project will accommodate all modes.”

img-capex-central-i35-expansion-austin-ladybird-lake-bridge-3

©TXDOT
The bridge crossing Lady Bird Lake will include a safe crossing area for pedestrians and bicycles. The design will ensure three lanes are always available during construction.

Efficiency to Maintain Capacity

Julian Summers, PE, senior vice president and project manager for WSP in the U.S., said one of the biggest challenges was designing the plans for the 1,000-foot-long bridge crossing Lady Bird Lake, a constant level lake that will require construction to take place in the water.

“We designed it in a way that the highway can maintain three lanes of traffic north-south – southbound or keep three lanes of interstate traffic each direction open at all times,” Summers said. “Our approach will allow the bridge to maintain its existing capacity through construction.”

Precast concrete pavement sections will be used for the first time on the interstate highway and will improve the project’s efficiency.

Precast concrete will provide a constant pavement type through the entire corridor. While it’s been done on smaller portions of roadways, Summers said this will be the first time that it’s done on the interstate.

Using those precast concrete pavement sections will allow the contractor to get in and out fast to avoid shutting down lanes for long periods of time.

Julian Summers Senior Vice President and Project Manager

Julian Summers Senior Vice President and Project Manager

Saeedi said the resulting highway will transform downtown city life along I-35.

“We’re providing better east-west connections; we’re providing shared-use paths; we’re providing accommodations for transit,” he said. “The impact that all of these upgrades will have on the quality of life for Austin motorists and residents alike will be profound.”

Meet the Visioneers

Julian Summers not only leads our design team for the CapEx Central project, but as a local resident who travels along this road regularly, he understands the struggles Austin motorists have long endured. As project manager, he is combining his skill and perspective to markedly improve mobility throughout the region.