On the west side the old wagon road over the top shows on goggle maps as #501. I drove it from Yankee Doodle Lake over the top
1984-1987(?) in a '64 Ford 4x4 pickup. The only problem was backing the rear tires to the edge of a cliff at a tight switchback designed
for horse wagons. It was closed to motor vehicles years ago above the closed tunnel (blocked years before by falling ceiling rock) at
at the RR grade above the tunnel down to Yankee Doodle Lake. Shows on google map satellite continuing down Jenny Creek towards
Rollinsville. It does bypass most of the RR grade.
Am sure you can hike over to the tunnel from the west side if you can't drive it in your vehicle. Much discussion 35'ish years ago in
Boulder and Forest Service to clear and stabilize the tunnel but nobody wanted responsibility for doing it or the ongoing maintenance.
Bring your camera!!