Castle Pines advances Happy Canyon I-25 interchange upgrades

Drivers using Happy Canyon Road and Interstate 25 in Castle Pines should expect a rebuilt interchange, a second bridge north of the existing span, and ramp and signal changes once construction starts in July 2026. The city says most of the work will happen outside the roadway, with traffic kept on Happy Canyon during bridge work, but commuters should still brace for temporary lane shifts, intermittent ramp closures and nighttime I-25 closures.

Castle Pines has selected Kraemer North America to reconstruct the interchange in partnership with Douglas County and the Colorado Department of Transportation. The project calls for replacing the existing bridge, adding a new bridge north of the current structure, rebuilding the I-25 on- and off-ramps, and making signal and intersection improvements throughout the corridor. City officials say the work is scheduled to wrap up in mid-2028.

The project is meant to do more than smooth out one choke point. City materials say the redesign is intended to improve traffic operations, connectivity and regional mobility while supporting growth around the northern Douglas County corridor. The preferred layout is a Diverging Diamond Interchange, which the city says was chosen over a Tight Diamond, a Single Point Urban Interchange and other alternatives because it can handle forecast 2050 traffic volumes and reduce conflict points. That matters for the daily stack-up at Happy Canyon and I-25, where turn movements, ramp merges and highway access all collide in one limited footprint.

The funding picture is still part of the story. In its 2025 open-house materials, Castle Pines estimated the preferred interchange concept at $36 million, with another $6.5 million needed from CDOT to replace the existing bridge, for a total forecast of about $42 million. Douglas County contributed $1.2 million in June 2024 toward redesigning the I-25 ramp at Happy Canyon Road, and county commissioners later approved another $500,000 for final design work. City planning materials also said future interchange construction had depended on funding from Douglas County and other partners.

The project has been building for years. Douglas County initiated the Happy Canyon Road/I-25 Improvement Project in 2015, Castle Pines moved forward with it in 2022, and a roundabout at Happy Canyon Road and Lagae Road was completed in 2024 as early work tied to the larger plan. City materials say the interchange concept has been evaluated against prior regional studies and is consistent with Castle Pines planning guidance as well as Douglas County’s 2040 Transportation Master Plan.

The interchange is also tied to future development pressure. Castle Pines says The Canyons annexation in 2009 approved 3,343 acres for up to 2.1 million square feet of mixed-use commercial space, 2,500 residential units and 1,400 acres of open space. A future connection to The Canyons via Canyonside Boulevard will be built by the developer and is expected to open after the interchange work is finished, leaving the new ramps and bridge work as the immediate fix and the broader growth network still waiting on the next phase.