Frequently Asked Questions

What is CDOT proposing for the Twin Tunnels area?
The Colorado Department of Transportation (CDOT) proposes widening the interstate to three eastbound lanes between Idaho Springs and the base of Floyd Hill, enlarging the eastbound bore of the tunnels and addressing safety issues on the eastbound highway curves between the tunnels and Floyd Hill. The project is approximately two and a half miles long.

The design of the proposed action would generally maintain the existing road geometry. The eastbound lanes would be widened at the outside edge by adding a new third lane to the south. In one location just east of Hidden Valley, the curve in the road would be straightened to allow drivers to safely maintain higher speeds. This curve is the location where the highest number of crashes occurs in the project area.

The Twin Tunnels Environmental Assessment (EA) will evaluate the impacts of two variations of the road sections, both of which will maintain the existing ten-foot shoulders on the south. They are:

• A 50-foot road section throughout the project.
• A wider 56-foot road section on the west end of the project from Idaho Springs through the tunnel to Hidden Valley, then a 50-foot road section east of Hidden Valley to the base of Floyd Hill. This variation provides a wider 10-foot inside shoulder (as compared to a 4-foot shoulder provided by the narrower section) through the tunnel.

What are the benefits of these design standards?
Both road sections would achieve the following goals:

• No encroachment of Clear Creek’s two-year or 100-year floodplains;
• No median encroachment that conflicts with the I-70 Mountain Corridor Context Sensitive Solutions (CSS) Design Criteria;
• Maintains or expands the vertical and horizontal separation of the eastbound and westbound lanes;
• Stays within the existing CDOT right-of-way, except at the existing chain station;
• Rebuilds the existing chain station west of the Twin Tunnels to meet I-70 Chain Station Plan requirements;
• Minimal walls visible from the roadway; no walls visible from the roadway exceed 12 feet (highest walls are approximately 7 feet);
• Meets I-70 Mountain Corridor CSS Design Criteria and Aesthetics Guidelines.

What is the purpose of the Twin Tunnels Environmental Assessment?
The EA will define the proposed improvements, provide information on impacts to environmental and community resources, and determine appropriate mitigation to minimize any impacts, following the requirements of the National Environmental Policy Act (NEPA). It is being conducted by CDOT and the Federal Highway Administration (FHWA). The FHWA is expected to issue a decision by the fall of 2012. CDOT is required by law and by the FHWA to complete the NEPA process before any construction occurs.

How will the process work?
The EA was initiated in September 2011 and is expected to be complete in November 2012.  Public outreach began in the fall of 2011, when the project hosted a public meeting to present background information about the proposed action, as well as to gather input about the NEPA process and timeline and environmental and social resources in the project area.  The project team has refined the proposed action and is currently studying the proposed action’s impacts on environmental and community resources, as well as evaluating measures to avoid or minimize impacts.  A public hearing on the study’s findings and recommendations will occur in July 2012.  The EA will honor all commitments in the I-70 Mountain Corridor Programmatic Environmental Impact Statement (PEIS) Record of Decision (ROD) and will comply with the I-70 Mountain Corridor CSS Guidance.

Why are you only addressing the eastbound lane and tunnel bore?
While improvements are needed in the westbound direction, eastbound improvements were prioritized because:

• Eastbound congestion is more pronounced and occurs over a longer period. Improvements in the eastbound direction would provide immediate relief for I-70 Mountain Corridor travelers.
• Crash history indicates greater safety concerns in the eastbound direction. More than 65 percent of all crashes in the Twin Tunnels project area occur in the eastbound direction.
• Westbound improvements will be more costly and com­plex to environmentally “clear” and construct due to the rock cuts and creek impacts that will result from realigning the westbound lanes. The cost of including the westbound lanes is far greater than the funding that is currently available.

Will CDOT use a Construction Manager/General Contractor (CM/GC) approach for building the Twin Tunnels project?
Yes, after conducting the required process to determine the project delivery method, CDOT decided to evaluate proposers and select the best qualified contractor to perform as the Construction Manager/General Contractor (CM/GC). This contractor will be part of the design and construction of the Twin Tunnels. The CM/GC process brings contractors into the planning and design phases, allows construction methods to be tailored to the contractor’s strengths, and provides flexibility and cost control early in the process. CDOT anticipates this process will save both time and money.

Why don’t you completely remove the mountain and the tunnels that go through it?
This concept was considered during the recently completed I-70 PEIS, but was screened out for a number of reasons. While the environmental impacts of removing the tunnels were not evaluated, the Twin Tunnels Wildlife Land Bridge is a known and important wildlife crossing.  It serves a critical role to bighorn sheep and other large game mammals. Blasting out this very large quantity of rock would likely have adverse environmental impacts, generate large quantities of waste materials, and create an area prone to rockslides and other geologic hazards that would be difficult to manage.