Dallas’ I-35E Lowest Stemmons Project Predicted to Greatly Increase Driving Speeds This Fall
Working Quickly in Tight Space: Collector-Distributor Roads Cost-Effectively Relieve Congestion and Boost Safety on I-35E in Dallas
The $79 million, 2.3-mile Lowest Stemmons project in downtown Dallas will improve traffic flow on one of the state’s most-congested highways – without any reconstruction or reconfiguration of main lanes.
On each side of Interstate 35 East, two collector-distributor lanes will run parallel to the highway. “A lot of weaving and merging occurs in that area with connections to the Woodall Rodgers Freeway and the Dallas North Tollway,” said Tony Hartzel, Public Information Officer Section Director for the Texas Department of Transportation (TxDOT). “The collector-distributors in both directions will give that traffic its own lanes to enhance operations and safety. The new lanes will act like a long exit ramp – without intersecting city streets like a frontage road.”
When the project finishes this fall, traffic is forecasted to travel much faster through the area. “We did a lot of study beforehand, including a microsimulation, to quantify the benefits of the project,” Hartzel explained. “Our consultant found that right now in that area, the average speed is 13 mph going northbound and 18 mph going southbound during peak morning rush hour. When the project is complete, speeds are estimated to be 50 mph.”
The microsimulation compared current traffic vs. 2028 traffic numbers (with the collector-distributors) and showed that the project will alleviate peak-hour congestion not just on I-35E, but also on Woodall Rodgers. “A little bit of concrete will go a really long way in improving the operations and safety,” Hartzel said. “It’s still $79 million, but it’s a lot less than totally reconfiguring the interchange.”
Funded by the Texas Clear Lanes initiative, the project received environmental clearance in May 2017 and let in June 2017, with the contract awarded to Balfour Beatty of Dallas. Construction work stretches from Interstate 30 to Oak Lawn Avenue and began in October 2017. In addition to the northbound and southbound collector-distributor roads built primarily on bridge structures, work includes direct connectors, reconstructed ramps, and bridges to accommodate the improvements. On the south side, the project will tie in with the Dallas Horseshoe project, completed in 2017.
Lowest Stemmons is a breakout project from the larger Lower Stemmons project that will extend on I-35E from State Highway 183 to Interstate 30. “We’re doing a feasibility study now for that corridor to look at options,” said Ceason Clemens, Deputy District Engineer for TxDOT’s Dallas District.
In the meantime, TxDOT leveraged existing funding to make the interim improvements. Although few collector-distributor roads currently exist around the state, “We’re starting to utilize them more and more where it makes sense,” Clemens said. “[In TxDOT’s Dallas District] they’ve been used on I-35E from Dallas to Denton City and within the Horseshoe project.”
In the Lowest Stemmons project, “One of the great things was that it required no right-of-way acquisition,” Hartzel said. “We worked within our right-of-way between I-35E and a major railroad freight corridor.”
Unfortunately, that created one of the project’s biggest construction challenges: “We squeezed the work in a very tight space,” Hartzel said. “It’s really a feat to watch the construction in such a confined area on both sides of the highway. There are no lane closures during peak hours, but we shifted the lanes on I-35E to provide a little more room to work.”
In one section of the work, an overhead electrical transmission line added to the constraints. “Prior to the project we raised that up, but crews still needed to use a low-profile drill rig for the bridge shafts,” Clemens said.
One corner of the project, adjacent to an old landfill, required special measures before building the new roadway. “We don’t have the best soil – there’s a lot of fat clay – so we’re using stone columns,” Clemens explained. “We used a shallower shaft and put aggregate in it to stabilize the soil in the approaches to the bridge structure. As soon as we get on the bridge, then we go to our traditional drill shafts.”
To complete some aspects of the work, the project team occasionally closed ramp lanes overnight. However, the American Airlines Center – home to the NBA’s Dallas Mavericks and NHL’s Dallas Stars – sits next to the site and created more limitations.
“If there’s an arena event, we won’t do any major closures overnight until all that traffic clears out,” Hartzel said. “Through basketball and hockey seasons, that’s been pretty frequent.”
To minimize disruptions and achieve the operational improvements as quickly as possible, TxDOT used A+B bidding (price plus time) in awarding the construction contract.
“There was a significant dollar amount on the B portion,” Clemens said. “Bidders told us how many days they could complete the project in, and each one of those days was worth $50,000. Balfour Beatty was not actually the lowest dollar bid, but their bid plus the number of days was lowest.”
To ensure the work finishes on time, the construction contract includes a $50,000 per day penalty for late delivery. “The sooner we get this project in, the better off the operations will be, and we’ll benefit the traveling public faster,” Clemens said.
With 240,000 vehicles passing through daily, the project area ranked as the eighth most-congested highway in Texas. When the Lowest Stemmons project finishes, “The collector-distributor roads will not only reduce congestion and increase speeds, but the big thing is the safety,” Hartzel said. “The collector-distributors are a very cost-effective way to do the same thing that expanding the roadway would’ve done.”