According to the Denver Post:
"The plane went down east of Vail, in between the resort town and the
10,666-foot summit of Vail Pass, said Suzanne Silverthorn,
community officer for Vail."

The question I have is why were they in that location? The
Eagle-Vail (EGE) airport is west of Vail. Following I-70 (Vail Pass) is
not exactly a good idea, due to the non-stop winding roads. No place
"straight" to land until west of Vail (which is why the airport
is west).

I can only think of 3 reasons- and remember, this is purely
conjecture. I know absolutely nothing more than what's been
reported:

1) scenic tour of the valley
2) student & CFI
3) they didn't know any better

Update from the NBC affiliate:
"EAGLE COUNTY - A Piper PA-32 crashed near I-70 at the summit of Vail Pass
Friday morning after trying to land in the westbound lanes of the highway.

The plane touched down on the highway, then hit some trees before
coming to rest on the mountainside about 25 feet up a slope,
said Jamie Wilson, a spokesperson for the town of Vail."

Assuming a 53F temp over there (I'm in Denver), at 11K, that means
13K density altitude. At ground level. At a reasonable flight
altitude of 12.5K to 14K, we're talking 15K-16.8K density altitude.

Current conditions are calm winds, 54F, vis 9 sm, clear sky. Winds have
either been calm or less than 7 mph since 8 pm last night.