If you’re a Front Range skier or boarder, you know this feeling well. You’re ripping turns at Keystone or Copper, and instead of being excited for the prospect of free refills when it starts nuking, you’re filled with dread. “We’ve gotta get out of here before they start metering the tunnel!” you shout to your friends. “Or worse, close it.”

But by the time you’ve hustled down the mountain, packed up your gear, and merged onto I-70 eastbound, it’s too late: You’re met with a river of red tail lights as skiers, truckers, and transcontinental road trippers wait first for the interstate metering light at Silverthorne and then the alternating lights at the mouth of the Eisenhower-Johnson Memorial Tunnel. But unlike the lights that manage on-ramps in and around Denver, these two lights aren’t about managing traffic flow to keep things moving smoothly. They’re there for one simple, if at times frustrating, reason: preventing traffic from backing up in the tunnels.

There’s a slew of reasons these “safety closures” are so important, says Bob Fifer, deputy director of operations at the Colorado Department of Transportation (CDOT). The first is carbon monoxide poisoning. “If people are sitting too long in the tunnel, even if they’re moving one or two miles per hour, it’s not enough to get air to flow correctly in there,” Fifer says. “So if everyone’s idling their gasoline vehicles or their diesel trucks, you could have a serious health issue.” The tunnels do have massive, multistory fans, but they aren’t enough to circulate air through the tunnels without an assist from moving traffic. Besides, turning on all the 50-year-old fans at once would temporarily disrupt power for others in the area, Fifer says.

One of the 50-year-old fans that circulates air inside the Eisenhower-Johnson Memorial Tunnel. Photo by Nicholas Hunt

If bad air quality wasn’t enough, there’s more medical rationale for keeping the tunnels clear: I-70 is the state’s major east-west artery, and it is the only way many living on the Western Slope can reach Front Range medical services they can’t access in the mountains, including specialists and advanced trauma care.

Fires that break out in the tunnel pose a unique threat. The tunnel staff has its own mini-fleet of fire engines, but their mission is only to contain flames that spring up until the real firefighters arrive. CDOT often chooses to stop people in Silverthorne rather than having them queue at metering lights at the tunnel entrance so first responders can reach incidents inside, if necessary. “If we have I-70 fully gridlocked,” Fifer says, “we will never get help.”

The other reason is that Silverthorne is a lot closer to services so people can eat, nap, and use restrooms while they wait. (It’s much more pleasant to wait out the traffic at Frisco’s Prosit with a pretzel in hand than hangry on the interstate.) The terrain is also flatter near Silverthorne, so if a car breaks down or there’s a wreck, response crews will have a much easier time sorting out the mess there than on the steep approaches on either side of the tunnel.

“One recent issue we’ve been having is electric vehicles running out of battery,” Fifer says. Instead of charging before the ascent, drivers think if they can just make it to the tunnel, they’ll recoup all that electricity on the way down the other side. Fifer says around six electric vehicles have petered out in the tunnels recently, and because their wheels can’t move when the battery is dead, CDOT has to coat the flatbed of a tow truck with a special lubricant so workers can slide the EVs onto it. Officials can spend more than half an hour clearing a stuck car from the tunnels. “We’re trying to get better at communicating why we’re closed,” Fifer says, “because people say they don’t understand. You’ll see the frustration on our part because we are scrambling to get the road open. It’s all hands on deck. There’s nobody just lounging around.”

Still, the goal is to stop traffic as little as possible—for every hour the Eisenhower-Johnson tunnel is closed, the local mountain communities that rely on it lose $1.6 million in economic impact from delayed shipments, lost tourism revenue, and more, Fifer says. Plus, for every minute traffic is stopped, it takes four minutes to get it moving again. That’s why it’s so important for drivers to follow not only the state’s traction laws but also those pesky on-ramp lights.

“The reason we do that is so the mainline [of traffic] keeps flowing,” he says, “because if everyone blows through that light and queues up into that merge lane, guess what? It doesn’t move.” Instead, Fifer encourages everyone to be patient. “Just calm down and let people merge because if you create a gap and you’re still moving, that means everyone else is still moving. Then we avoid that gridlock.”

Nicholas Hunt
Nicholas Hunt
Nicholas writes and edits the Compass, Adventure, and Culture sections of 5280 and writes for 5280.com.