Perhaps you’ve sat in Interstate 70 mountain traffic and wondered why Colorado hasn’t built a passenger train to the ski resorts from Denver. While state and local governments have considered a train, it’s a complicated solution.

Experts long ago determined that conventional rail won’t work because the hills are too steep. And while new technologies, like maglev, which is a train system that utilizes magnets, might handle the steep pull, the constraints for public transportation along I-70 are physical as well as fiscal.

Any mountain transit or highway project confronts geology and geography. The canyons are extremely narrow, and rock fall and avalanches sweep off the steep hillsides despite state efforts to control them. Historic sites line the corridor. Wild animals already struggle to cross the busy highway, and many die trying. Streams and creeks flank the roadway, so any construction project must prevent pollution and erosion. Towns — like Idaho Springs and Dumont — could be destroyed if the transportation corridor is widened either for transit or new traffic lanes.

The Colorado Department of Transportation already wrestles with an approximately $9 billion statewide project backlog because funding hasn’t kept pace with growth. Colorado hasn’t raised its gas tax, which helps fund transportation projects, since 1991. The tax has been a flat 22 cents per gallon of gasoline for nearly three decades, and CDOT estimates its buying power is half as much as it was thirty years ago when adjusted for inflation.

In the same time frame, the state’s population soared from about 3.3 million to nearly 5.8 million people. And despite widespread bellyaching about traffic, voters rejected a pair of transportation-related ballot measures in 2018 as well as another ballot proposal this November.

Still, transit in I-70’s mountain corridor remains on CDOT’s wish list. In 2014, the agency performed a technical feasibility study of Advanced Guideway System solutions, which are different technologies that would follow a set track. One option the state considered is some form of a train.

The limitations imposed by the steep grade and tight curves, however, showed that any potential alignment for a rail-based system can’t use the highway median. The hills, nearby creeks, wildlife habitat and proximity of towns like Idaho Springs to the highway all complicate any plans.

“Many of these concerns must be considered, no matter the technology: highway, passenger rail or other,” says David Krutsinger, CDOT’s director of the Division of Transit and Rail.

But the state can’t just add new highway lanes, he notes.

“The line of logic has been that if Colorado looks fifty years into the future and had a highway-only expansion approach, there would potentially be more impact from six-, then eight-, then ten-lane highways, rather than providing a rail line, [with] capacity [that] could be increased by adding to each train's length and/or increasing the frequency of trains,” Krutsinger explains.

I-70 from Golden to Vail — the stretch of road that gets most of the ski and summer tourist traffic — isn't crowded most of the time; high use occurs on weekends and holidays, but even then doesn’t match vehicle volumes on other major Colorado roads. For example, some 2,900 cars drove eastbound through the Eisenhower-Johnson Memorial tunnels during the busiest hour of September 29, 2019 (the most recent day for which CDOT has information). But the next day, a non-holiday Monday, the busiest hour of eastbound traffic registered less than half that volume, just over 1,000 vehicles.

I-70’s mountain traffic also peaks during months with holidays: In January 2018, about 1.2 million vehicles traveled through the tunnels, while in July 2018, more than 1.4 million cars and trucks did so. By comparison, Interstate 25 between Fort Collins and Denver carries 175,000 cars and 4,300 bus transit riders every day, or more than 5.25 million travelers (mostly back-and-forth commuters) every month. As a result, CDOT prioritized addressing the nearly continuous traffic nightmare in Weld and Larimer counties — plans that include more public transit — as well as improvements to other consistently used corridors such as I-25 south of metro Denver. (Note: CDOT isn’t responsible for the long-delayed commuter rail link from metro Denver to the Boulder/Longmont area; that project falls to the Regional Transportation District.)

“It's a balancing act,” Krutsinger says of CDOT’s long-range transit plans. “The I-25 Front Range Corridor would have more [transit] ridership due to five days a week of strong usage due to commuting, versus I-70 Mountain Corridor with two to three days of weekend recreation traffic.”

CDOT, however, has implemented several improvements that make the mountain drive safer, if not faster.

Downhill from Idaho Springs, CDOT spent $175 million widening the tunnels that previously caused numerous accidents and notorious traffic jams. Today the wider, renamed Veterans’ Memorial Tunnels include better lighting and other upgrades so drivers don’t slow down as much when entering them, which has prevented major backups.

Traffic also used to stall inside the higher-altitude, larger and longer Eisenhower-Johnson tunnels — posing a serious safety risk in case of an accident or fire. Now, CDOT limits the number of vehicles in the tunnels at any given time, reducing the chances of rear-end collisions and fires. During peak periods, drivers may wait twenty minutes for traffic to clear, but because the cars and trucks have more space, their drivers maintain steadier speeds and avoid lane-weaving — making the drive much safer but about 3.5 minutes longer, CDOT data shows.

CDOT is now focusing on reconstructing the notoriously jammed-up Floyd Hill segment, says CDOT Chief Engineer Steve Harelson. The $600 million project entails building three westbound lanes to the Veterans Memorial Tunnels, extending the frontage road from U.S. Highway 6 to the Hidden Valley exit, reconfiguring both the U.S. 6 and Hidden Valley interchanges, and flattening (or making less tight) several substandard curves.

I-70 drivers today still face slow-downs and construction detours, but future journeys should be safer and more pleasant. Just don’t expect a rail system anytime soon.