Drivers in south Castle Rock have a full interchange on Interstate 25 at Crystal Valley Parkway as of this month. The Town of Castle Rock says the project is now open nearly eight months ahead of schedule, with the southbound ramps finished in November 2026 and the northbound ramps in service since July.

The town has wanted an interchange at this spot since the 1980s, and it calls the Crystal Valley project the largest of its kind in Castle Rock's history. It was built by the town together with Douglas County and the Colorado Department of Transportation.

What is open now

The interchange came together in stages over almost three years, and each piece is now in place:

  • A roundabout at Crystal Valley Parkway and East Frontage Road, east of I-25, finished in January 2025, along with a relocated East Frontage Road shifted east to make room for the ramps.
  • A new Crystal Valley Parkway bridge over both the BNSF Railway tracks and I-25, which opened to east-west traffic in November 2025.
  • Dawson Trails Boulevard, a new road west of the railroad tracks with a signalized intersection at Crystal Valley Parkway. It replaced the old West Frontage Road, which closed permanently when the bridge opened.
  • Northbound on- and off-ramps east of the interstate, opened in July 2026. They gave this part of southern Castle Rock its first direct northbound access to I-25.
  • Southbound ramps west of the interstate, built along the old West Frontage Road alignment and tied into the bridge through a new signal. These were the last piece, completed in November 2026.

Landscaping and other finishing work outside the travel lanes will continue into early 2027, so expect some crews along the edges through the winter.

Why it matters for a daily drive

The town says the interchange improves access and safety from the south end of Castle Rock down to the Tomah Road interchange, and it lists three goals for the new connection: a better local road network, one fewer railroad crossing for drivers to use, and a new east-west route across the interstate.

The bridge over the BNSF line matters on its own. Taking traffic over the tracks rather than across them removes an at-grade crossing from the daily routine of everyone who used the old West Frontage Road.

What it cost and who paid

The full project, including design, right-of-way purchases and construction, came to about $144.7 million. The town lists these contributions:

  • $53.6 million from developers
  • $24 million from Douglas County for the interchange, plus $11 million for the road that became Dawson Trails Boulevard
  • An $8.9 million grant from the Denver Regional Council of Governments
  • A $5.4 million federal BUILD grant from the U.S. Department of Transportation
  • $1.7 million in town electric credits
  • $900,000 from BNSF Railway

The balance comes from the town's Transportation Capital Fund, which draws on sales tax, motor vehicle taxes, impact fees on new development, taxes on construction materials and contributions from neighboring developments. Castle Rock voters also authorized the town to put revenue above its state TABOR limit toward the interchange.

How the schedule ran

Final design wrapped up in 2023 and construction began in early 2024. The town now lists November 2026 for completion of the full interchange, nearly eight months ahead of the schedule it had been working to.

Getting there

The interchange sits on I-25 at the south end of Castle Rock, north of the Tomah Road interchange. From the west side, Crystal Valley Parkway connects through the new signal at Dawson Trails Boulevard; from the east side, it runs through the roundabout at East Frontage Road.

Questions about the remaining finishing work go to the Crystal Valley interchange project team at 720-733-6097, and the town posts project updates on its Crystal Valley Interchange page.

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