officials plan to convert a dormant underground tunnel into pedestrian walkways, creating an alternative people-moving system so that air travelers and workers no longer have to rely on DIA’s trains for reaching concourses.
Design work will begin this year on the project to repurpose this existing baggage tunnel, adjacent to a tunnel that carries the electric trains, at an estimated cost between $300 million and $700 million, Denver Mayor Michael Johnston said. Johnston planned to announce the plans on Tuesday morning. Construction is scheduled to start next year, with the 17-foot-wide walkways opening in 2028.
DIA’s trains broke down 262 times over the past two years, airport records show. While most of the breakdowns were brief, lasting an average of four minutes, DIA officials say the lack of a backup option as the airport grows, toward a projected 120 million travelers a year by 2045, increasingly causes problems.
Repurposing the tunnel, built before the airport opened in 1995, “gives us the most affordable and fastest way to solve the challenge,” Johnston said.
“The whole world has speculated for decades about what exists in the tunnels under Denver International Airport. Now, the whole world will get to see it,” he said, referencing conspiracy theories that include bunkers under the airport to protect the global elite in case of an apocalypse or even evidence of aliens.
For more than five years, DIA chief executive Phil Washington has been exploring options for creating a backup system to minimize disruptions and missed flights when trains break down at the airport, the third-busiest in the United States and sixth-busiest in the world.
DIA’s team initially considered replicating the pedestrian A Bridge, a 365-foot link between the terminal and the A Concourse. A new bridge connecting concourse A to B would have to stretch 1,400 feet, and a bridge connecting B to C would have to stretch 1,100 feet.
Denver officials said they haven’t ruled out building new bridges. But those construction projects would be far more disruptive than repurposing the underground tunnel, take longer to complete, and cost $2 billion to $3 billion, Johnston said.
Travelers choosing to walk along two one-third-mile walkways could move from the main terminal as far as Concourse C in 10 to 15 minutes – and faster if designs include moving sidewalks, Washington said.
“We want to make this a pleasing journey,” and artwork will be displayed in the tunnel. “We will make sure folks want to walk down there. It won’t be a dark alley.”
Over the past few months, city and airline officials have been discussing details. Airlines strongly support the effort to increase reliability in the airport so that train disruptions don’t cause travelers to miss or be late for flights, Washington said.
“We’ve had a must-ride train for 30 years. Now we see this as a must-have,” he said. “We are atoning for the original sin at (DIA) of not having redundancy.”
No excavation or tunnel boring is required. Travelers won’t notice the construction underground, Johnston said. Funding will come from airlines and airport revenues. “No taxpayer dollars” will be tapped, he said.
A broader $2.1 billion overhaul that has complicated DIA for more than five years should be finished next year with the opening of a new Great Hall. DIA officials plan more upgrades over the next 12 years, costing roughly $12.8 billion, with new runways and up to 111 more airline gates.
DIA is simultaneously carrying out a modernization of the 30-year-old automated underground trains, a $148 million project to expand train capacity and reduce wait times. Train contractors recently completed a partial fleet replacement, shifting from older steel cars to 26 aerodynamic white cars made of recycled aluminum.
Half of the 131 train breakdowns over the past year involved the new train cars, as reported recently by .
The modernization includes upgrading the signal and control system, which should also increase the train frequency.
The trains run 24/7 and, factoring in the breakdowns, operated 99.9% of the time over the past 12 months, DIA spokeswoman Courtney Law said.
But even brief breakdowns can cause havoc. On March 18, trouble at an Xcel Energy substation caused a power outage lasting about an hour that prompted the to ground all flights to DIA. The outage froze the trains.
“That day is seared into my memory. The escalators stopped. The elevators stopped,” said Washington, who has been exploring options to install a mini nuclear power station at the airport to further increase reliability.
The March train breakdown strengthened the resolve of city officials to create an alternative people-moving system as soon as possible by repurposing the tunnel, Johnston said. “We saw the urgency of having the solution come online faster.”
