I think it depends on the kind of commuting. I go to my school every day by train and bus which is generally a two hour ride. Since I don't have to drive myself, I can use this time to get a lot of work done. Although sometimes it can get frustrating if you have to do something with line-art, because bus tends to be not so steady.
Depends, but yeah, if you don't have to change lines then you might be able to get away with doing some work in transit. I did a commute by train that long, but it took me across a few different lines and so I couldn't really do anything during the trip ... except perhaps read. Still, by the end of the week, I was falling asleep on the return journey, regardless, because of how much the long commutes took out of me. I was continually sleeping late on the weekends to catch up. It's not a good idea long term; I'd suggest that if you are doing a commute of similar length and NOT sleeping more on weekends then you're operating on a large sleep debt.
I had a bike accident seven years ago. I shattered the bones in my right arm really badly. I spent 43 weeks in cast and it never really fully healed. I can still feel it when I lift heavy things and such stuff. The thing is, I was biking every day again the semester after the accident, when I was still in cast. Accidents happen. I do suppose that the traffic climate is much different here in Holland; bikes outnumber cars here.
That's the problem with injuries: you will feel them for the rest of your life.