One of Bob Brown’s earliest childhood memories is traveling with his parents through a notoriously complex maze of tricky interchanges, bridges and roadways in downtown Dallas known as the Mixmaster interchange.
Today the antiquated Mixmaster is gone—completely overhauled and replaced with the Dallas Horseshoe, a $798 million interchange that substantially improves the flow of traffic crossing the Trinity River along Interstate 30 and Interstate 35 to enter or exit the city’s downtown.
“Almost everybody that drives through Dallas uses this interchange, and for many people, it can be several times a day,” said Brown, who served as principal-in-charge for WSP USA on the project. “Those drivers are now experiencing significantly faster travel times.”
The original intersection, built in the late 1950s, was deteriorating and ill-equipped to handle the estimated 450,000 to 500,000 vehicles that pass through on a normal weekday.
“The left-lane exits at the interchanges and its odd geometry created a lot of weaving in and out of the lanes,” Brown said. “Now there is less weaving, less congestion, and the roadway is much safer for motorists.”
As the lead engineer, WSP was responsible for designing all of the roadways, bridges, river crossings, retaining walls, drainage, geotechnical engineering, and maintenance of traffic planning. The firm was teamed with Pegasus Link Constructors, a joint venture of Fluor Enterprises and Balfour Beatty, for the design-build contract to create the Dallas Horseshoe on behalf of the Texas Department of Transportation (TxDOT).
“The Pegasus Link team created an innovative maintenance of traffic plan that provided efficient working areas throughout construction that kept the traffic moving and minimized the impact on drivers using the interchange,” Brown said. “It was extremely important to TxDOT that road closures were limited, and our phased approach made sure that lanes were never shut down, other than intermittent overnight closures for demolition and bridge work.”
Design on the Horseshoe began in 2013, and construction began in January 2014. The Horseshoe was substantially completed on schedule in April.
While the Dallas Horseshoe simplifies travelling for motorists, to reach that point required complex planning and constant coordination between the designers and builders.
WSP and Pegasus Link made more than 70 geometric refinements to the plan during construction, each time to ensure that they were able to stay on track with build the roadways from the outside lanes inward, allowing motorists to continue using the old lanes until the new ones were completely ready for traffic.
“We were constantly assessing the progress of the project, providing ideas to see where we could improve traffic flow while keeping on track with construction,” Brown said. “Some ideas that may not have worked early in the process, but later on made sense, were added to the plan – especially when we could combine multiple operations within the same phase to limit lane closures.”
The Dallas Horseshoe included the construction of more than 73 lane miles of new roadway, 37 conventional bridges, more than 60 retaining walls, and two signature steel suspended arch bridges designed by world-renowned architect Santiago Calatrava.
With its distinct twin arches that rise 350 feet above the Trinity River, the 1,125-foot-long Calatrava-designed spans create what is now known as the Margaret McDermott Bridge, with 10 lanes of traffic carrying I-30 across the river. The bridge also incorporates pedestrian and bicycle lanes on either side of the bridge that connect to the city’s growing network of pedestrian trails.
“There was a significant amount of design collaboration required between the design-build team and the Calatrava team,” Brown said. “It was an unusual situation, but it worked out very well, and the result is an amazing bridge design for Dallas.”
The Dallas Horseshoe has been recognized with two awards for its design and overall improvements to transportation in the region.
The Design-Build Institute of America selected the project for a 2017 National Award of Merit in Transportation.
The American Council of Engineering Companies (ACEC) of Texas named the Dallas Horseshoe the winner of the 2018 Engineering Excellence Award gold medal for transportation. The project will be eligible for a national ACEC award next year.
The awards reflect the positive feedback that Brown has been hearing from the TxDOT, as well as Dallas city officials.
“TxDOT staff had a big interest in making sure that safety and mobility were always the focus, while the Dallas city staff was interested in making sure that the downtown, the Convention Center, and all of the city’s attractions were always accessible,” Brown said. “It was a great team effort, and being able to exceed everyone’s expectation made it even more special.”
Best of all are the comments he hears from those motorists who benefit from the improved interchange every day.
“The final product not only relieved Dallas traffic congestion, but did so with an infrastructure that was both aesthetically pleasing and cost-effective,” Brown said. “To have been a part of that effort from the beginning, and to see the benefits that it is creating, has been quite rewarding.”
Work may have come to an end on the Dallas Horseshoe, but WSP is already working with TxDOT and Pegasus Link Constructors on the next major project improve roadways near the city.
As the lead designer for the Southern Gateway design-build project, WSP is providing roadway, drainage, bridge, retaining wall, traffic, hydraulic/hydrology, maintenance of traffic and geotechnical engineering for the reconstruction and widening of Interstate 35E from Colorado Blvd to U.S. Route 67, and the widening of U.S. Route 67 to Interstate 20. The project includes non-tolled express lanes and high-occupancy vehicle lanes.
The 11-mile improvement project connects to the south of the Horseshoe and includes construction of a deck park near the Dallas Zoo that will require provision of fire-life safety elements. Design work on the $550 million project began in August.
“The success of the Dallas Horseshoe was a key reason we were selected for the Southern Gateway project,” Brown said. “We are looking forward to continuing that success with the same team that worked so well together on the Horseshoe.”