Crystal Valley Parkway and Plum Creek Boulevard Roundabout

Challenge

The Town of Castle Rock, Colorado, faced increasing traffic and safety concerns at the intersection of Crystal Valley Parkway and Plum Creek Boulevard. An existing two-way, stop-controlled intersection was no longer adequate for the amount of arterial and collector traffic it served, and did not meet the area's growth projections. Steep roadway grades exceeding seven percent added another layer of complexity, creating safety concerns for drivers, pedestrians, and cyclists.

As the Town worked to address these challenges, leaders also took a proactive approach – prioritizing stronger multimodal connections, planning for future traffic growth, and keeping the work within the existing right-of-way to limit property impacts. 

Solution

SEH collaborated with the Castle Rock to transform the intersection into a modern roundabout that improved traffic operations, enhanced safety, and met the community’s growing needs. Achieving these benefits on the site’s steep grades required a thoughtful approach that guided every aspect of the design. The team developed solutions that addressed vehicle safety, drainage, and visibility, while also making the intersection accessible for pedestrians and cyclists. By balancing technical demands with community priorities, the design created a safe and efficient intersection tailored to Castle Rock’s unique topography. 

Improving Multimodal Connectivity 

To enhance connectivity, the project added ADA-compliant and slip-resistant sidewalks and crosswalks alongside on-street bike lanes. On-street bike lanes transition to shared use paths via curb cuts at the intersection to avoid bicycle and vehicular conflicts. Roadway grade adjustments with utility relocations enabled ADA cross-slopes to be met for crosswalks, and solar-powered rectangular rapid flashing beacons provide added visibility. These features made the area safer and more welcoming for people walking or biking, while supporting the commitment to multimodal transportation. Drivers benefited from smoother traffic operations with less delays, while pedestrians and cyclists gained reliable routes that connected them more easily to the surrounding community.  

Building on these mobility improvements, the project also delivered key infrastructure upgrades to support the roundabout’s long-term performance. New drainage swales and storm sewer system improved drainage, while watermain and storm sewer lowerings ensured utility systems functioned without conflict. Updated street lighting, landscaping, and irrigation restoration further enhanced the safety and appearance of the intersection.  To limit disruption, the team used subsurface utility engineering (SUE) for precise utility coordination and conflict avoidance, and provided a phased construction approach to keep traffic moving and minimize impacts to commuter traffic.

Engaging Stakeholders for Project Success

Collaboration between project stakeholders extended beyond design and construction. SEH worked closely with community leaders, property owners, and the public to anticipate challenges and build support. Surveying, traffic studies, and utility geotechnical investigations guided design decisions, while temporary construction easements (TCEs) were negotiated to allow work to move forward efficiently. Public information efforts helped stakeholders and residents understand the benefits of the project and what to expect during construction.

The result is a safer, more efficient intersection that addressed today’s traffic needs while preparing Castle Rock for continued growth. By delivering improvements for drivers, pedestrians, and cyclists alike, the project strengthened community connections and provided lasting value for the Castle Rock and its residents.