It's one way for the full 2 weeks... It still gets busy... Don't be fooled by the video.. But it really does sum up what it's like over there. It's like wacky bike races when everyone scrambles to their race viewing point around the track.
Mate it's been one way since at least 1987, but only on the mountian back then and there wasn't all the 30/40/50 mph limits between the towns back then either. On mad Sunday you couldn't move almost for bikes and in all the years I went I never saw a car on the mountain on that day either.
I'm pretty sure you could also get to places that you no longer can on race days, it was pretty much go where ever you wanted back then but then like most things it's all become more regulated and comerical. The Classic was called the Manx GP a much more relaxed affair which now is almost as big as the TT now days, all that said its still for me the best racing in the world