A major Summit County traffic corridor is expected to get far busier in the next two decades, according to the results of a recent study commissioned by the Colorado Department of Transportation.
By 2045, experts predict traffic along U.S. Highway 6 and Colorado Highway 9 in the towns of Dillon and Silverthorne will increase by 45%. While an influx of motorists is likely inevitable, a number of potential solutions also exist to help mitigate congestion and safety issues, they said.
During a May 21 Summit Board of County Commissioners work session, transportation department officials joined representatives for Stolfus — the consulting group that conducted the study — to present their findings and recommend next steps.
The corridor has been a growing pain point for motorists for years, with eastbound and westbound exits for Interstate 70 creating traffic jams that have led local officials to call for an overhaul of the area. In particular, Exit 205 in Silverthorne has been seen as the epicenter of some of the worst vehicle backups, most recently during this past Martin Luther King Jr. Day weekend when the area became the epicenter of what officials called a “traffic nightmare.”
“We really wanted to look at the entire corridor to understand how operations will work for the entire corridor and not just at the (I-70) interchange itself,” said Michelle Hansen, vice president of consulting services for Stolfus. “That included corridor operations, safety, sustainability and the ability to work within both the built and natural environments within the area.”
The study attributes the projected growth in traffic to several factors including increased redevelopment that could add new housing and hotels, more commuters and growing interregional recreation.
But it does not recommend expanding highway lanes as a solution.
“The big reasons really have to do with the kinds of impacts we would see,” Hansen said. “Impacts to private property, businesses, impacts to how people can cross (Highways) 6 and 9.”
The highways are already “somewhat of a barrier for our pedestrians and our cyclists,” Hansen said, adding, “It was not a desire to make that barrier stronger and was just generally not compatible with Silverthorne and Dillon’s visions for what they wanted their communities to be like.”
Instead, one suggestion is to reduce accidents along the corridor that are often caused by high-risk movements, such as turning left into and out of a side street, Hansen said.
To do this, the study recommends potentially extending left-hand turn lanes and adding more right-hand turn lanes for certain side streets. It also suggests raising the median along the corridor, which can provide more comfortable left-hand-turning pockets.
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Commissioner Eric Mamula asked how traffic could be kept away from side streets that are used by residents, adding that during incidents when out-of-town motorists use those streets to try to cut around traffic “that completely throws out that (ability) for locals to use local streets.”
Hansen said it goes back to making access to and from the corridor safer for drivers, adding, “That will keep the traffic moving on (Highways) 6 and 9.”
Additionally, Hansen said improving walkability and bikeability along the corridor could incentivize alternative modes of travel that reduce the number of vehicles on the road. Ideas included making pedestrian crossings safer, closing gaps between sidewalks, better connecting trail systems and offering alternative pedestrian routes that don’t require crossing the highway.
Hansen added some local projects aimed at improving pedestrian safety have already been proposed by some towns, such as in Dillon, where officials have outlined a plan to build five roundabouts on Highway 6 to make it easier for pedestrians to cross at interchanges.
Another proposal is to evaluate traffic signal times more routinely to ensure traffic light intervals are “consistent with the various traffic patterns that are out there,” said Stolfus senior project manager Andrew Amend.
In 2023, CDOT implemented new timing plans for traffic lights along the corridor based on new data. The result was a 17% increase in traffic efficiency, or travel time, during peak hours, Amend said.
As traffic inevitably increases, regular review of traffic signal intervals will be imperative to managing vehicle flow, Amend continued.
“As you get redevelopment, all it takes is one really popular new place to pop up and then all of a sudden that traffic pattern in that area can change,” he said.
Commissioner Tamara Pogue said she heard from many community members last year who experienced longer wait times along the corridor after signal intervals changed.
Pogue asked, “Why would the public perceive something different when the timing has clearly improved speeds?”
Amend said the reason could be because the timing of traffic signals, especially during peak periods on weekends, favored motorists exiting onto I-70.
“If you’re a local and you’re just trying to get through on the interchange, you may have been delayed a little bit longer because more priority was given to that big left turn movement and getting that traffic flushed out of there,’ Amend said.
Officials also discussed a major proposal to reroute Stephens Way so that it connects with Little Beaver Trail and creates a new four-way interchange on Highway 6.
The proposal, depending on its design, could cost anywhere from $13.5 million to $26 million and was found to have mixed results when it came to cost and safety benefits, the study found.
While it could help traffic flow for drivers who are currently forced onto Highway 6 to get to either road, it could bottleneck adjacent intersections and make it more difficult for traffic to reach I-70, Hansen said. She added the area does not currently have a major issue with accidents, meaning the interchange likely wouldn’t have an impact on safety.
Because the cost of the project was not determined to provide enough benefit, Hansen said it would not be eligible for federal or state funding.
Hansen said some of the other proposals could be eligible for grant funding and recommended county officials work across towns and agencies to identify opportunities.
“I think as much as agencies can work collaboratively for funding recommendations, the better,” Hansen said.
