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Southeast Corridor Transportation Expansion Project (T-REX)

Artist rendering of a light rail station

Southeast Corridor Transportation Expansion Project (T-REX)
Denver, Colorado

Multimodal Design-Build Transportation Project

With a volume of more than 230,000 vehicles each day, the Interstate 25 (I-25) corridor, through Denver is one of Colorado’s most congested highways. In 2000, a national study of traffic issues identified metro-Denver as the seventh most congested metropolitan area and the I-25/I-225 interchange as the 14th busiest interchange in the country.

Parsons was selected as part of a joint venture team to design and build the Southeast Corridor Transportation Expansion Project (T-REX), the largest transportation contract in Colorado history. This multimodal design-build project includes highway, light rail transit, pedestrian, and bicycle facilities along the I-25 and I-225 corridors in Denver. As design manager, Parsons is responsible for approximately 50 percent of the total project design.

View from above of the interchange during construction

Construction under way at the I-25/I-225
Interchange

The design scope comprised civil and structural design, including permanent and temporary (detour) facilities, transit buildings, transit parking, and traffic maintenance during construction. Highway design involved improvements to 17 miles of I-25 and I-225, and included reconstruction of the University/I-25 and I-25/I-225 interchanges, upgrades at eight other interchanges, 60 bridges, and drainage enhancements. Additional highway capacity was achieved by adding one through-lane in each direction along the northerly portion of I-25 and on I-225, and by adding two through lanes in each direction along the southerly portion of I-25. For this project, more than 350 retaining walls were designed and built, a total of more than 2.2 million square feet of retaining walls. Additionally, three-quarters of a million square feet of sound walls were designed and constructed, many with wall art.
Tunnel boring machine poised at the entrance

Tunnel boring machine
startup at entrance portal

Parsons' design team provided an innovative reconfiguration concept for the I-25/I-225 interchange. This design moved light rail trains from the highest level of the interchange to the lowest level resulting in significant cost savings, aesthetic improvements, and improved temporary traffic control.

An important feature of the I-25 reconstruction is the I-25/Mississippi Avenue outfall. Approximately 3,000 feet long, the outfall conveys stormwater away from the I-25 and Logan bridge intersection. On any given day, heavy rains flood and strand travelers, who have coined the name "Lake Logan" for this area of the interstate. A 12-foot-diameter section of the outfall under Mississippi Avenue, about 800 feet long, was constructed using an earth pressure balance (closed mode) tunnel-boring machine. Parsons' design alternative reduced the length of the alignment by one third— avoiding costly right-of-way acquisitions— and diverted the tunnel away from potentially hazardous materials along the original route.

Parsons was the primary designer of 19 miles of double-track light rail transit along I-25 and I-225 including 13 new transit stations, park-and-ride lots, three new parking garages, a new operations control center, power and signal systems, and a supervisory control and data acquisitions system for the existing transit lines. These highway and transit improvements bring long-term transportation relief for some of metro-Denver’s fastest-growing and most congested areas.

T-REX included more than $60 million in intelligent transportation system (ITS) elements. Parsons was the primary designer of the ITS, including dynamic message signs; CCTV cameras; freeway and arterial detection (to monitor surface street congestion); ramp metering; a communications network; an Interim Traffic Management Center housing an incident information management system; and public information Web channels. During the construction phase, a project web site, www.trexproject.com, informed the public of real-time traffic conditions.

View of the completed exchange from above

Completed I-25/I-225 corridor

By the end of 2002, design for T-REX was 85 percent complete and construction was 25 percent complete.  Construction of the light rail line began in Spring 2003. And by Fall 2006, the T-REX project concluded - nearly two years earlier than was requested by the client.
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Project Details (featured in Feb 2003)

  • Client:

    Colorado Department of Transportation and Regional Transportation District

  • Project Construction Cost:

    $1.16 billion

  • Project Duration:

    2001–2006

  • Project Details:

    Design Management, Civil/Structural Design, Permanent/Temporary facilities, Light Rail Design, ITS Design, Post-design Service

Location

Credits

  • Photos:

    Photography on this page was provided by Gregg Gargan, CDOT.