Operating on orders to double the capacity for traffic mobility, but design “no higher and no wider,” design firm Bridgefarmer & Associates worked tirelessly over the course of five years to complete the I-635/LBJ Managed Lanes project in Dallas.
A project that had been on TxDOT’s books for nearly three decades, the I-635/LBJ Managed Lanes project reconstructed the freeway’s eight existing general-purpose lanes and added six new managed, depressed lanes in an excavated trench section.
“I-635 was one of the worst-congested freeways in the country for many, many years,” Mansoor Ahsan, P.E., CEO of Bridgefarmer & Associates, told Roads & Bridges. “And TxDOT has tried to widen the corridor many times, and simply couldn’t because it’s fully developed.”
For the 17-mile project, Bridgefarmer proposed the concept of a “no tunnel option” or “open cut” solution for the project. The innovative concept became the solution as a result of the restrictions TxDOT mandated for the project to be built no higher than existing lanes on the interstate and no wider than the existing right-of-way, due to the placement of a plethora of businesses and housing developments along the corridor. In addition, the open cut became a less expensive solution than the originally proposed tunnel option.
What made the open cut practical for the Bridgefarmer team was that it enabled them to simply design one span, and then repeat that design for each section of the project.
“If I am mobilized for one span, I can repeat it a hundred times or a thousand times,” Ahsan said. “Our team did exactly that; we came up with one span, and we repeated it throughout the corridor.”
A significant challenge for the managed lanes project was keeping lanes open throughout construction. “TxDOT required that the existing number of lanes be maintained the majority of the time,” Project Manager Lisa Deitemeyer told Roads & Bridges. “So we had to set our alignments so that we could phase the job in such a way that we could maintain the number of lanes of traffic and build a new corridor of roadways, bridges and walls—that was a big challenge of the job.”
Opening a year earlier than anticipated, toll revenues along the LBJ since completion of the project in September 2015 indicate significant improvements on the corridor, since revenue has been much higher than originally anticipated. Since the freeway moved 270,000 vehicles per day prior to construction, Bridgefarmer & Associates anticipates that the new managed toll lanes will be capable of withstanding 500,000 vehicles by 2020.
Location: Dallas, Texas
Owner: Texas Department of Transportation
Designer: Bridgefarmer & Associates Inc.
Contractor: Trinity Infrastructure LLC
Cost: $2.7 billion
Length: 17 miles
Completion Date: September 2015