Client:
Colorado Department
of Transportation
and Regional Transportation District

Project Construction Cost:
$1.16 billion

Project Duration:
2001-2006

Parsons Services:
design management; civil and structural design, including permanent and temporary (detour) facilities; light rail design; ITS design; post-design services

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 fourteenth busiest interchange in the country.

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

The design scope comprises civil and structural design, including permanent and temporary (detour) facilities, transit buildings, transit parking, and traffic maintenance during construction. Highway design involves improvements to 17 miles of I-25 and I-225, and includes 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 will be 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, over 350 retaining walls are being 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 will be designed and constructed, many with wall art.

Rendering of reconfigured I-25/I-225 Interchange

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 rain floods and strands 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—and avoided costly right-of-way acquisitions— and also diverted the tunnel away from potentially hazardous materials along the original route.

Left: Tunnel boring machine startup at entrance portal Above: Tunnel boring machine breakthrough at exit portal

Parsons is 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. Once complete, these highway and transit improvements will bring long-term transportation relief for some of metro-Denver’s fastest-growing and most congested areas.

Rendering of light rail vehicle at new Arapahoe Station

T-REX contains over $60 million in intelligent transportation system (ITS) elements. Parsons is 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. Currently, during the construction phase, the project web site, www.trexproject.com, informs the public of real-time traffic conditions.

Completion of the T-REX project is scheduled for fall of 2006, nearly two years earlier than required by the client. At the end of 2002, T-REX’s design was 85% complete and construction was 25% complete. Construction of the light rail transit line is scheduled to begin in spring 2003.

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