Happy Canyon Interchange

Project Overview

Safety improvements are coming to the Happy Canyon Road and Interstate 25 (I-25) interchange in Castle Pines. The proposed improvements, consistent with the City of Castle Pines Comprehensive Plan and Transportation Master Plan guidance, will also improve traffic operations, connectivity, and regional mobility, as well as support local community growth. This project also aligns with the Board of Douglas County Commissioner’s Core Priority to provide a reliable multi-modal transportation network. This project is identified in the County’s 2040 Transportation Master Plan, and it’s one of the County’s priority projects as identified in the County’s current 5-Year Capital Improvement Program.

Approval of the surrounding developments has been contingent on interchange improvements and incorporates connections with the surrounding regional road network, such as Crowfoot Valley and Hess roads.

The preferred alternative shown below, referred to as a Diverging Diamond Interchange (DDI), is being evaluated by a joint effort between the City of Castle Pines, Douglas County, the Colorado Department of Transportation (CDOT), and the Federal Highways Administration (FHWA).

Diverging Diamond Interchanges are an innovative approach to traffic design, offering improvements in safety and efficiency. These interchanges excel in managing heavy directional traffic, ensuring smoother flow and reducing congestion in high-volume areas. Left turn movements are typically the most risky and least safe movements through an interchange. With a DDI, CDOT reports that these dangerous T-bone accidents are eliminated by removing the typical left turn movement.

Benefits of a diverging diamond:

  • Reduces delays using a two-phase signal as opposed to a traditional four or six-phase signal.
  • Requires fewer lanes but can handle more traffic capacity.
  • Reduces conflict points at intersections.
  • Improves pedestrian crossing safety with easier access to medians.
  • Increases left turn capacity.
  • Eliminates wrong-way entry to ramps.
  • Costs less than a typical free-flow interchange utilizing single-directional flyover ramps.

How to drive a diverging diamond interchange:

Watch this video from the Colorado Department of Transportation for more information on driving through a diverging diamond interchange.

Funding 

The Happy Canyon Interchange Project is currently identified in the Denver Regional Council of Government’s (DRCOG) long-range 2050 Metro Vision Plan, and the City was recently allocated pre-construction funding through the DRCOG Transportation Improvement Program (TIP) project selection process.  The DRCOG allocated Federal Funds (Surface Transportation Block Grant) are being matched with City and County funds to advance NEPA, design and other pre-construction tasks.

Construction costs are forecasted to be $34 million. Douglas County has identified $20 million in its current Transportation Capital Improvement Program 5-Year list of priority projects. The remaining construction funds will be from the City of Castle Pines and developer contributions.

Furthermore, it is estimated an additional $6 million is needed from CDOT, if CDOT elects to replace the existing Happy Canyon bridge over I-25 as part of the local agencies overall interchange improvement project. CDOT has rated the existing bridge as in need of replacement or upgrades, but CDOT has several other bridges throughout the State that are also in need of major repairs. However, the City and County will continue to pursue funding from CDOT for replacing the existing bridge, as well as pursue other grant funding opportunities.

Schedule

A Public Meeting will be held in early 2025. You will have an opportunity to review and comment on the preferred alternative via the project website and/or in person.

Happy Canyon Interchange Project Schedule

Happy Canyon Interchange Resource Documents 

Background and History 

In 2015, Douglas County initiated the Happy Canyon Road / I-25 Improvement Project to identify long-term interchange improvements, which included 2030 and 2040 traffic projections, alternatives analysis, and development of conceptual design plans for various interchange alternatives. Revised traffic modeling was necessary to update the Castle Pines Parkway & Happy Canyon Road Final System Level Study (Aug 2009).

In 2022, the City of Castle Pines elected to move forward with managing the Happy Canyon Interchange Project and advance improving the connection from I-25 to both Lagae and Happy Canyon roads. This connection and roundabout were completed in summer 2024. The City continues to work closely with the County, CDOT, and FHWA to finalize the System Level Study that evaluates the existing and future traffic operations utilizing 2050 traffic projections.

Using CDOT’s Policy Directive 1601 Interchange Approval Process several strategies have been developed that facilitate mobility options to help reduce the number of single-occupant vehicle trips. This is accomplished by promoting and implementing strategies, programs, and alternative modes of travel which include carpooling, walking, encouraging tele-working, transit, and biking.

Utilizing 2050 traffic projections, the City and its consultants identified four alternatives to improve the interchange, The four interchange alternatives evaluated include:

  • Tight Diamond with Traffic Signals at the I-25 Ramps
  • Tight Diamond with Roundabouts at the I-25 Ramps
  • Single Point Urban Interchange (SPUI)
  • Diverging Diamond with Traffic Signals at the I-25 Ramps

The Diverging Diamond Interchange (DDI), shown above, is the preferred alternative to move forward through the National Environmental Policy Act (NEPA) clearance process and into preliminary and final design.

The Tight Diamond Interchange options studied cannot provide acceptable operations for the forecasted 2050 traffic volumes, meaning that this option would not provide traffic alleviation. Although the SPUI can operate with the 2050 volumes, it is estimated to cost $10 million more than the DDI. It was determined that the DDI alternative will better accommodate the 2050 traffic projections than the Tight Diamond with Roundabouts at the I-25 Ramps alternative, which were previously determined to adequately handle the 2040 traffic projections.

Exhibits of these alternatives can be found in the I-25 and Happy Canyon Road Interchange Alternative Analysis.

Frequently Asked Questions (last updated December 2024)

Why are improvements at I-25 and Happy Canyon Road needed?

The proposed improvements at Happy Canyon Road and I-25 Interchange will improve safety, traffic operations, connectivity, and regional mobility, as well as support local community growth. Improving access to and from I-25 is an important element of the proposed project. Improving I-25 access will improve safety and traffic operations while reducing both delays and the congestion associated with accommodating the 2050 traffic projections.

When was it determined that improvements to the Happy Canyon interchange were needed?

Improvements at the Happy Canyon interchange have been included in regional and local plans since 2001. For several years, regional and local plans identified the need to add left turn lanes at the interchange to improve traffic operations. Additionally, these plans noted that shoulders or a second through lanes could be added to make the interchange more reliable and continue to operate safely when crashes occur.

Approval of adjacent nearby developments has been contingent on interchange improvements and incorporates making connections with the regional road network, which includes Crowfoot Valley and Hess roads.

Are developers paying for the improvements at I-25 and Happy Canyon?

Improvements at the Happy Canyon interchange have been included in regional and local development plans for several years. Approval of the surrounding developments has been contingent on interchange improvements and making connections with the surrounding regional road network, which includes Crowfoot Valley and Hess roads.

The current opinion of construction costs is forecasted to be $34 million. Douglas County has identified $20 million in its current Transportation Capital Improvement Program (CIP) 5-Year list of priority projects.  The remaining construction funds will be from the City of Castle Pines and developer contributions

Additionally, CDOT is responsible for replacing the existing Happy Canyon Road bridge over I-25, which is estimated to cost an additional $6 million if it is included with the local agencies proposed interchange improvement project.

When can I talk to the project team about the improvements?

In addition to the proposed public meetings early next year, the City will maintain a project website that allows the public to review project information and provide public comment.

Public comments received through this website will be included with all the other comments received during the project public meeting (open house format).

Will traffic be impacted during construction?

Yes, traffic on I-25 and at the ramps will be impacted during construction of the interchange improvements. Although impacted, access is expected to be maintained during the project.  Neighborhoods will always have access during construction. Detours are possible during construction. Traffic delays should be expected.

The answer to this question be more detailed as the project moves forward, therefore, updates will be provided as the design progresses. During construction, the contractor will be charged with providing any changes in the lane configurations and the most up-to-date traffic impact information, including dates and times.

Why not lower the speed limit to reduce hazards in our area?

There is a common misconception that posting a speed limit will influence drivers to drive at that speed. The facts indicate otherwise. Studies show that a driver’s speed is influenced more by the appearance of the road and the prevailing conditions than by posted speed limits, and, in fact, unrealistically low speeds can actually cause accidents.

However, the design team and the Colorado Department of Transportation will evaluate when and where to consider implementing speed reduction zones during construction.

Stay informed on the progress of this project: