A sinkhole that turned out to be a collapsed railroad tunnel has indefinitely closed Highway 24 near Leadville.
After announcing Tuesday morning they'd reopen one lane to passenger vehicles, the Colorado Department of Transportation decided Tuesday afternoon the road just isn't safe. It is now closed between Red Cliff and Leadville in both directions.
A sinkhole measuring 20 feet by 30 feet around and more than 100 feet deep collapsed Monday afternoon, causing CDOT crews to close the road.
All motorists will be detoured to State Highway 91. Crews marked and barricaded the sinkhole from the highway, but decided Tuesday that the sinkhole could expand and that it wasn't safe to allow motorists anywhere near it.
There is no estimated date to reopen the road.
"After looking at it all day Tuesday and seeing how it did with cars driving over it, our engineers decided it was not safe for motorists," said Ashley Mohr, CDOT's regional public relations manager. "It's not a disaster right now, and we don't want it to become one."
The Highway 24 sinkhole is deeper than crews thought - they originally estimated it to be about 45 feet deep.
The sinkhole is actually a century-old abandoned railroad tunnel that collapsed decades ago, CDOT engineers, maintenance supervisors and geological experts determined.
The tunnel was built between 1900 and 1910 and ran under Tennessee Pass, but collapsed when the wood beams supporting it gave away.
No one is exactly sure when that tunnel collapsed, but Union Pacific Railroad built another tunnel in the 1940s, Mohr said. The newer one is lined with concrete and is doing just fine.
CDOT engineers have been all over that sinkhole Monday and Tuesday, and learned all sorts of interesting stuff.
When that original tunnel collapsed, it filled with all kinds of earth and rock.
Since the hole reached so far into the earth, much of the soil was still frozen until recently. The hot weather finally finished melting it and it collapsed Monday, Mohr said.
Federal highway officials built U.S. Highway 24 right over that collapsed tunnel and it's been driven over ever since.
No one is certain if highway engineers at the time knew about the collapsed tunnel, or even if Union Pacific knew about it, Mohr said.
CDOT engineers and maintenance crews used mirrors Tuesday morning to bounce around reflections of the sun, all the way to the bottom of the sinkhole. That enabled them to get an accurate measurement.
They're not sure if the collapsed tunnel runs level. But at the deepest point they've found so far, it's about 100 feet deep, Mohr said.
They're not sure when it will be repaired, or even what it will take.
About 45 feet down, the hole starts to curl back under the highway, Mohr said.
The sinkhole is almost exactly halfway between Red Cliff and Leadville, on the north side of Tennessee Pass.
In June 2003, a 20-foot sinkhole collapsed the westbound lane of Interstate 70 above East Vail. Hundreds were evacuated from their homes overnight.
That one shut down a 24-mile stretch of I-70 between Copper Mountain and Vail.
For real-time updates about road conditions and the sinkhole in our area, go to www.coloradodot.info.