Press Coverage

42 csengineermag.com august 2019 The MoPac Expressway intersections at Slaughter Lane and La Crosse Avenue in southwest Austin were originally constructed in 1992. Since that time, Austin's population has nearly doubled, according to the U.S. Census. Average daily traffic on the MoPac Expressway, which was 21,000 in 2010, is projected to reach 66,700 by 2030. As a result, the intersections at Slaughter Lane and La Crosse Avenue became congested over the years, creating operational problems, caus- ing travel delays, and affecting access, safety and mobility. In 2013, the Central Texas Regional Mobility Authority and the Texas Department of Transportation (TxDOT) initiated an environmental study to analyze and determine options for reducing travel delay and enhancing safety at these intersections. "During the morning and evening peak hours, motorists had to wait through multiple traffic signal cycles at these two intersections," said Lucas Short, P.E., TxDOT's project manager. Following the study and public review, TxDOT decided to construct underpasses at Slaughter Lane and La Crosse Avenue and extend the MoPac main lanes under these two intersections. The MoPac main lanes, two in each direction and approximately two miles long, would be constructed inside the existing MoPac lanes. The existing Mopac lanes would be reconstructed and serve as ramps to carry main lane traffic to Slaughter Lane and La Crosse Avenue. The grade separation at La Crosse Avenue and MoPac was config- ured as a standard diamond interchange while the grade separation at Slaughter Lane and MoPac was configured as a diverging diamond interchange (DDI) – the first in the city of Austin and the second in the Austin area. Other improvements include constructing an additional 10-foot-wide shared-use path on the west side of MoPac from Slaugh- ter Lane to La Crosse Avenue, retaining walls at the bridges, a storm sewer system, traffic signals, new pavement, and striping and signing throughout the project limits. "The improvements will reduce delays for northbound and southbound traffic in the MoPac Expressway as commuters don't have to stop at a signalized intersection to travel through the area," said Short. "Also, constructing the DDI at Slaughter Lane will allow for more efficient left turn movements." To implement these improvements, TxDOT selected Lockwood, An- drews & Newnam, Inc. (LAN), a national planning, engineering and program management firm, as the lead design engineer. Kimley-Horn and Associates, Inc. was selected as the traffic control plan and tempo- rary signals sub-consultant, Cobb Fendley and Associates, Inc. as the illumination sub-consultant, and IDCUS, Inc. as the drainage, signing and striping sub-consultant. In August 2017, the project went to letting and Webber was awarded the contract as the low bid. TxDOT Builds a Rare Diverging Diamond Explosive Growth in Austin Triggers Novel Traffic Solution By Bob Austin, P.E. The Diverging Diamond Interchange is gaining popularity because of its efficiency and safety. Photo: LAN

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