Texas S-curve

May 22, 2024
A one-of-a-kind, network tied arch bridge connects trails in Dallas

By Suze Parker, Contributing Author

Installed in a single night, the Northaven Trail Bridge links several bike and pedestrian trails above U.S. Route 75, an eight-lane highway in north Dallas.

The project provides a safe crossing for users, extends recreational opportunities and expands access to alternative modes of transportation.

Before the bridge opened in November 2023, the popular Northaven Trail on the west side of U.S. Route 75, as well as the Cottonwood Creek and White Rock Creek trails on the east side, essentially terminated at the roadway.

To cross one of the busiest highways in Texas and access the trails on either side, cyclists and pedestrians had to use a poorly lit and often muddy underpass.

The Texas Department of Transportation (TxDOT) called the bridge “a regional example of the positive benefits of appropriate location and design aesthetics for future bicycle and pedestrian trails and amenities.”

The bridge also links to the DART Light Rail Station at Forest Lane. Where challenges existed before, now stands a beacon to alternative transportation.

A Community’s Vision Comes Alive

Lee Kleinman, a former Dallas city council member, proposed the idea for a pedestrian bridge over the highway in the early 2000s.

The Dallas Parks and Recreation Department, the Friends of Northaven Trail group and others joined the council member in championing the project.

TxDOT engaged HNTB to serve as conceptual designer, engineer of record and construction phase services provider on the project.

The project entailed a large public outreach effort to stakeholders, including trail users and communities and organizations located near the trails, to gather input on the community’s needs and wants.

That public engagement work provided a look at the desires of the communities on each side of U.S. Route 75 and began to inform geometry of the trail bridge and how it needed to function.

When Kleinman proposed the pedestrian bridge, he was inspired by the idea of representing a bicycle wheel in its design. The original network tied arch concept for the main span was developed in 2017 by HNTB to reflect all stakeholder feedback.

The network cable arrangement, a term used when the cables cross one another more than once, also reduces bending in the arch and deck, allowing each to be thin while still being resilient to accidental overloads.

In this case, the Northaven Trail Bridge uses 64 cables— 32 per side. This design is also reminiscent of the spokes on a bike’s wheel.

“It’s surprising how much the final design adhered to some of the early sketches and modeling concepts developed from conversations with the city of Dallas and other stakeholders,” said Tom Kramer, HNTB project manager. “Often, an early concept and what is ultimately built are quite different. In this case, we developed a unique initial concept and saw it all the way through.” 


The site designated for the Northaven Trail Bridge has a unique geometry that required the bridge to be built at an angle across the eight mainlanes and four frontage road lanes of U.S. 75.

A reverse tied arch structure was developed to give the bridge a soft, reverse “S” curve, which reduces the skew at the piers. As typical of tied arches, the bridge deck ties the ends of the arch ribs together, like the string in an archery bow.

"With tied arches, that 'string,' or the deck, normally must be straight," said Kira Larson, HNTB project manager of construction phase services. “However, in the Northaven Trail Bridge, we see an S-curve geometry. Within that S-curve are straight post-tensioning strands running through the deck, acting as the tie. It’s a highly innovative way our design team created this signature project for TxDOT.”

The structure is the only known network tied arch bridge in the world with a doubly curved tie. The bridge also has skewed ends, making it an incredibly complex structure not seen anywhere else.

Keeping the Traveling Public Moving

TxDOT’s two critical priorities during construction were the structure’s integrity and public safety. A key project goal was to deliver the bridge with minimal impact to the traveling public.

The agency required that a frontage road lane or a lane northbound and southbound on U.S. 75 remain open throughout construction. They also required that any mainlane closure period be limited to overnight on Saturdays.

Those requirements drove early design choices to employ accelerated bridge construction techniques, which allowed the bridge to be built off-site and moved into place.

The structure selected was a lightweight, redundant system that could be safely transported to its final location on self-propelled modular transporters (SPMTs). The bridge was constructed on timber shoring in the back parking lot of a nearby furniture store.

“An accurate design was provided for the project in order for us to safely construct it with minimal change orders or plan revisions,” said TxDOT Dallas County area engineer Nathan Petter. “Because this was such a unique bridge, challenges came up that we had to work through during construction. We were able to find solutions every step of the way.”

Larson said that communication was crucial to the project because of the structure’s complexity.

“When changes needed to be made at the construction site, the team would quickly collaborate to find solutions,” Larson said.

When COVID-related supply chain issues delayed material deliveries, recommendations were made that reduced fabrication lead times.

In the case of cable adjustments, turnbuckles were selected that allowed cable tension to be adjusted in a few turns without the cable being disconnected every time a tension change is needed.

An Overnight Bridge Shift

Moving the entire bridge into place with SPMTs was a first for TxDOT’s Dallas district. On a September night, team members stood side-by-side on U.S. 75 watching the 201-foot-long, 800,000-pound Northaven Trail Bridge with its 50-foot-tall arch be driven into place over the highway.

SPMTs shouldered the structure at its bearing locations and lifting gantries moved the bridge into place. The installation procedure included:

  • Gantries are erected on either side of the piers along U.S. 75, with gaps left for the SPMTs.
  • SPMTs lift the bridge from where it was constructed in a nearby parking lot and drive it to the highway, adjacent to the piers.
  • Gantries lift the bridge off the SPMTs.
  • SPMTs are removed from under the bridge.
  • Gantry track is pinned and completed.
  • Gantries roll the bridge south to hover above the piers.
  • Bridge is lowered onto its final bearings.
  • Installation equipment is removed.

Moving the bridge took about 20 hours but required only about 14 hours of full closures on the mainlane, Petter said. During that time, traffic was diverted to the adjacent frontage road, leaving a lane of traffic always open to drivers.

After the bridge was installed, final tie-ins were completed before the span opened to the public.

Striking Architecture, Heavy Use Demonstrate Project Success

With a structural weight of 800,000 pounds, the Northaven Trail Bridge is designed to withstand a pedestrian load of approximately one person per square foot of bridge deck, or approximately 445,000 pounds.

The bridge’s cable arrangement was carefully designed to increase the structure’s stiffness by a factor of 10, making it incredibly resilient to accidental overloads.

“The day the Northaven Trail Bridge opened, tons of people were using it,” Petter said. “The public was so vested in this wonderful project. The use we immediately witnessed showcases the project’s success.”

TxDOT also created dedicated parking on the west side of the bridge for anyone who wants to drive to the site and use the spot as a trailhead. The parking area is designed as a space that could accommodate food trucks, the start of a race, or other events.

Because the bridge’s arch is its most identifiable feature, it has quickly become a defining landmark that serves as a gateway into north Dallas. Feedback provided to TxDOT reveals that the public is in awe of the benefits it has already brought to the community. RB

Suze Parker is a public relations consultant and writer who frequently writes about roads, bridges and other infrastructure projects. 

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