Ha I never came across this thread first (or second) tme round. I cycle through the tunnel a couple of months ago and was disturbed to see a barrier across. The last time I cycled through must have been in the late 1990's early 2000's... I don't recall any chalk lines though they're may have been I wasn't looking out for them.
I'd have to do this on My Dawes Galaxy (with rack) as its the heaviest bike I own.