Interstate 25/Colorado State Highway 402 Interchange Design-Build

Reconstructing I-25: a massive undertaking

The design-build project aimed at reconstructing 14 miles of Interstate 25 (I-25), including overhauling three full interchanges. The Colorado State Highway 402 (CO 402) interchange was critical, acting as the main gateway from I-25 to the City of Loveland and enduring substantial truck traffic.

The challenge of CO 402 interchange

The existing CO 402 interchange presented a unique set of challenges. It was a tight diamond configuration with I-25 passing over it and a frontage road on the east side, immediately adjacent to the interchange. This compact layout was further complicated by substandard horizontal and vertical curves on I-25, which raised significant safety concerns.

Safety and traffic operation improvements

The project required a complete reconstruction of the interchange to enhance safety by standardizing the curves of I-25 and improving traffic flow at the three intersections involving the southbound ramps, northbound ramps, and the frontage road. The timeline was constrained by a strict 120-day closure of CO 402, with no closures permitted for I-25 or the ramp connections from CO 402.

Innovative solution by RS&H

In a display of innovative thinking, RS&H proposed completely flipping the interchange, having CO 402 pass over I-25. This strategic change, combined with the adaptable nature of roundabout geometry, allowed the team to shift the roundabouts and the crossroad southward. This shift facilitated the construction of a perpendicular bridge crossing over I-25 that could be built offline, thus avoiding a full closure of I-25.

The revised design enabled the construction of a single-span bridge, which was completed swiftly, reopening CO 402 well within the 120-day limit. Implementing free-flowing roundabouts further enhanced traffic operations, even with the challenging constraints of the interchange and frontage road configurations.