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TxDOT Continues Loop 360 Underpass Construction in Austin

by: Debra Wood
A retaining wall is constructed along southbound Loop 360 at Riverbend Church. Pennybacker Bridge is visible in the top of the photo.
A retaining wall is constructed along southbound Loop 360 at Riverbend Church. Pennybacker Bridge is visible in the top of the photo.
Crews remove rock adjacent to the existing roadway.
Crews remove rock adjacent to the existing roadway.
Crews work on a retaining wall and frontage road.
Crews work on a retaining wall and frontage road.
Drainage work takes place along Loop 360.
Drainage work takes place along Loop 360.
Crews removing rock from the project site.
Crews removing rock from the project site.
Team members review work taking place near the Pennybacker Bridge.
Team members review work taking place near the Pennybacker Bridge.
Crews construct a retaining wall along northbound Loop 360 at Davenport Ranch.
Crews construct a retaining wall along northbound Loop 360 at Davenport Ranch.
The Texas Department of Transportation (TxDOT) has embarked on a $72.1 million construction project at two Austin’s Loop 360 intersections.

“The project will improve safety and mobility at the Loop 360 intersections of Westlake Drive and Cedar Street by constructing an underpass, where the Loop 360 main lanes go under the cross streets,” says Brad Wheelis, Southwest Communications Director for TXDOT.

A major north/south transportation corridor for the Austin capital area region, Loop 360 serves as a thoroughfare and commuter route for residents. Increased safety concerns have cropped up due to traffic congestion and the lack of mobility on this route.

“With more than 2 million people who live in the Austin area today, and expectations that that number is expected to double by 2040, we can expect traffic congestion to worsen,” Wheelis says.

Lowering Loop 360
The existing Loop 360, while part of a beltway around Austin, has two lanes in each direction and surface-level intersections with cross streets. TxDOT plans additional improvements to the 14-mile-long corridor, eliminating at-grade crossings and signals, as part of the Loop 360 Program. The corridor is one of the state’s most congested roadways and is considered a scenic route.

Located near the landmark, steel-arch Pennybacker Bridge, this project will remove those signalized intersections, separating the grade between Loop 360 and Westlake Drive and Cedar Street by lowering Loop 360; adding adjacent two-lane wide frontage roads, with shared-use paths for pedestrians and bicycle traffic, on each side of the Loop 360; adding U-turns at Westlake Drive to connect the frontage roads; relocating utilities; and constructing bridges to carry traffic on Westlake Drive and Cedar Street over Loop 360. All of the work takes place in existing right of way.

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“In 2020, the average daily traffic Loop 360 was 52,050,” Wheelis says. “Nearly 14,000 daily users travel the Westlake Drive/Cedar Street project corridor, many with destinations within the work zone.”

TxDOT reports, “Westlake Drive at Loop 360 is the most congested intersection along the corridor,” increasing safety concerns.

Additionally, many people bicycle along the route, often riding on the Loop 360 shoulders. This new configuration is designed to separate vehicular and bicycle traffic.

TxDOT and the City of Austin’s 2016 Mobility Bond have funded the construction. Voters approved $720 million in bonds for transportation improvements.

WSP of Austin, Texas, served as the design engineer for the project. The engineering, environment and professional services firm provides technical expertise and strategic advice to clients in transportation and infrastructure, property and buildings, environment, energy and water sectors, as well as offering project and program delivery and advisory services.

The engineers and TxDOT considered multiple options for improving the road, including taking Loop 360 over Westlake Drive and Cedar Street. But ultimately, the public wanted Loop 360 to go under the local streets, which is what TxDOT decided to do, even though it would be more difficult due to the need to excavate through solid limestone rock.

“We take pride in having done the design for such an iconic stretch of highway,” says Arash Saeedi, WSP Local Business Leader, based in Austin. “We are super thrilled to be part of it.”

HNTB, with offices in Austin, performs construction engineering and inspection for TxDOT on this project.

Completed Construction
COPASA with offices in Miami, Florida, received the construction contract and broke ground in June 2022. The company is based in Spain and has offices in Asia, Europe, and North and South America.

“Crews are working on numerous assignments concurrently throughout the corridor,” said Victor Vargas, PE, Senior Construction Manager for HNTB.

During the summer of 2023, crews completed cliff cuts along the northbound Loop 360, near Bold Ruler Way. Crews continue removing rock. More recently COPASA completed construction of a U-turn near Bold Ruler Way.

“The opening of the U-turn happened in coordination with the closure of the original Waymaker Way crossover,” Vargas says. “This work helps improve safety along the corridor.”

Other notable accomplishments include the construction of a retaining wall at Steeple Chase and a storm sewer installation at Westlake Drive and southbound Loop 360, Wheelis adds.

TxDOT flies drones to take periodic photos of the corridor to monitor progress over the course of the project.

Future Challenges
In October 2023, COPASA was reconstructing the Westlake Drive intersection with northbound Loop 360.

“Crews are working to raise the profile of the intersection, while constructing retaining walls, installing utilities, and removing the original median island, to name a few tasks,” Vargas says.

Much of the construction work remains in the days ahead. Additional rock excavation is under way along southbound Loop 360 near the Pennybacker bridge.

“A future challenge on this project will be the reconstruction of both the Westlake Drive and Cedar Street bridges,” Vargas says. “Both bridges are traditional, however, there are milestones associated with the construction of each in order to efficiently re-establish cross street traffic.”

Crews will use the existing rock walls and in places, install soil-nail walls and mechanically stabilized earth retaining walls.

During construction, traffic will be detoured to the next closest U-turn opportunity, north and south of the construction zone.

“The milestone for the Westlake Drive bridge is 109 days and for the Cedar Street bridge the milestone is 147 days,” Vargas says. “The construction of the bridges will not happen concurrently to mitigate traffic impacts.”

TxDOT anticipates the project will complete in mid-2025, weather permitting.

“We always enjoy partnering with TxDOT on this and look forward to the remaining phases of the 360 corridor being built out,” Saeedi concludes.

Photos courtesy of Texas Department of Transportation