WSP USA is completing the design phase of the USD $798 million Dallas Horseshoe Project, a complex road interchange through the city’s central business district.
WSP is lead designer to the design-build contractor, Pegasus Link Constructors (PLC), a joint venture of Fluor Enterprises and Balfour Beatty Infrastructure, which is performing the project on behalf of the Texas Department of Transportation (TxDOT). WSP is designing replacements for the roadways and 45 new bridges for the Interstate 30 and Interstate 35 interchange. The firm will also oversee the quality, completeness, schedule, and cost of all design deliverables. Work on the project began in April 2013, and initial design work will be fully completed this May.
Becky Fly serves as project manager and Bob Brown is principal-in-charge. Design staff from more than 10 WSP offices in the Central and Mountain regions contributed to the project.
Rated one of the most congested roadways in Texas, the I-30/I-35E corridor carries as many as 460,000 vehicles a day and is one of the largest interchanges in the state.
“With the original interchange being built in the late 1950s, the current expansion has been a long time coming,” Fly says.
Construction began in January 2014. When completed in 2017, the Horseshoe Project will improve traffic flow in downtown Dallas and add capacity to the interchange and frontage roads.
Fly says the new design adds additional lanes to the interchange in the hopes of reducing the daily bumper-to-bumper rush hour gridlock that has plagued these roadways. It will improve traffic flow through better signage and by eliminating confusing transitional lanes that often result in drivers crossing several lanes to reach their exits. The Horseshoe Project also expands existing high occupancy vehicle lanes to encourage fewer vehicles on the roadway.
Managing the daily traffic that will continue to use the Horseshoe during the next three years of construction was one of the key challenges designers faced. To minimize the impact, Fly says construction is starting with permanent construction of the outer lanes of the project and will proceed inward, with traffic detoured in the newly completed outer lanes until each section is completed.
Fly says the design team decided to make one change from the original pursuit, increasing the number of bridges from 40 to 45. The new bridges were the result of splitting longer bridges in two and using a fill plug between the two sections, when it was advantageous and less costly to do so.
“As with any opportunity to work hand-in-hand with our contractor team, the project changes to maximize the efficiencies of the construction and minimize the costs,” she says.
Another challenge with design was the need to construct some of the road structures over three major Dallas Water Utilities wastewater lines in conflict with proposed drilled shafts. To address this, straddle foundations will be used above the tunnels to provide support for the bridges while maintaining the acceptable clearances and avoiding impact to the existing tunnels.
The Horseshoe project is exclusively using concrete girders for all of the bridges, including the incorporation of four 73-to-82-meter- (240-to-270-foot-) long spliced girder spans on six of the bridges over the Trinity River. There are three locations where multiple bridges cross one another. Fly says a ladder design is being incorporated, where the bridges will stack on the “rungs” of the structural support. This design reduces the number of foundations needed to construct the bridges.
Fly says some of the spliced girder bridges crossing the Trinity River had the added challenge of being designed to provide foundation support for the Santiago Calatrava-designed pedestrian bridges to be constructed as part of the project.
WSP will continue to provide design services for the project through its completion.