This tunnel was proposed to be bypassed in 1951. This proposed line was called the "airline" and it was to bypass the sharp grades. The feature of the proposed line was a proposed 6,165' bridge over the Mississippi near Bellevue, which would have a 650' cantilevered main span, with numerous 245' and 303' deck truss spans. What a bridge this would have been!
I'd probably go in late December, so snakes wouldn't be out. And 3/4 mile isn't that bad. I've walked a mile and a half down an abandoned rail grade for a railroad bridge before....
According to waymarking.com it's a 3/4 mile walk and parking is suggested at N 42° 20.034 W 090° 23.182
Watch out for rattlesnakes if you make the trek up there. It's a beautiful landscape, but rattlesnakes are known to be present in the area.
Is it a Pretty hair raising walk back there?
It is still possible if you go from the West, however the entrance to the tunnel is barricaded as the east end was filled in. Enjoy the hike up to it, though.
Is it possible to access this bridge still?
There used to be a large bridge just east of Blackjack Rd leading back to the tunnel entrance. I crossed it and hiked back there with a buddy of mine in the early 80's. There's large iron bridge parts on a property along Sandhill Rd right nearby I assume were parts of this bridge.
The east portal has been sealed in, but the west portal still exists. However it is in a very isolated area and is in bad condition. The tunnel is now owned by the Illinois Dept. of Natural Resources and access to the tunnel has been cutoff due to the risk of further collapse.