Thanks for everyone's good wishes and sorry for not replying a little sooner. I've been sleeping a lot. Funny how an injury can make you tired.
To answer various questions & comments:
mtnwalker - The bridge is a drawbridge, so I think the gap I caught was the one between the two halves, perpendicular to the road. My best guess is that I was at a shallow enough angle to it as I crossed from the right lane to the left that my tire was able to turn a little and fit into the gap, tossing me for a real fun ride. Too bad I was not conscious to enjoy it, huh? ;-) Still, Boston's mayor is pretty bike friendly and you may be on to a good idea about seeing if something can be done about it.
Chris Pringle - The only reason I made the lane change when I did was because there were no cars for a good distance behind me. I often have to wait until traffic is stopped at the light where I need to turn in order to weave between stopped cars to get safely over to the left.
slcbob - I plan to visit the spot again, if for no other reason than to perhaps get a better understanding of what happened. I'll try to remember to get a photo and post it.
Doohickie - I wonder if I would have continued to commute if I had crashed as early on as you. On the other hand, I was considering getting on the bike and continuing home until the ambulance showed up the other night.
bergerandfries - Very good point. Like I said, Boston's mayor is very bike friendly. Hopefully we can get something done. If nothing else, we can get better crash data for statistical purposes?
capejohn - I have followed the helmet debate on and off for several years. I agree with those who say that wearing a helmet can lead to riskier behavior, but I also think that the helmet really did help me this time. Seeing the chunk missing from the helmet right where my forehead is (and still is) was proof enough for me. Ultimately, I think that it is the decisions I make (like perhaps not changing lanes on that drawbridge?) that lead to my safe riding. Stuff like the helmet, lights, and reflect-y clothing are all gravy that help make it a little safer. You're absolutely right though, I'm okay. And that IS the bottom line.
AdamDZ - I actually have 2 bridges like this on my commute. I can only avoid one of them, but to do so takes me over much more hilly terrain. To go my normal route is much flatter and faster. Maybe someone is telling me to try interval training for a while? ;-) BTW, I've had the same thought about falling in front of traffic.
A few other comments:
I have always worn my helmet. I consider it equivalent to the seat belt in a car or an American Express card. I just don't leave home without it.
Tires. My front tire is a Michelin something-or-other. It's a 1.3". Not the skinniest, but not the widest either. I plan on switching it out for a Schwalbe Marathon when it wears out. My rear tire is already running the Schwalbe. I prefer my tires to be relatively high pressure so I can go faster. My bike is heavy enough and my commute is long enough that I need all the help I can get.