I've crashed a couple times due to trolley and train tracks, even though I'm usually pretty aware of them. The last one was on a trip to Santa Fe -- I fell pretty hard at the beginning of a ride but thought I just had a sprained wrist, so I did the 50 miles I had planned. When it refused to get better, my wife the M.D. said "Yeah, you probably broke it. It'll heal." No sympathy at all! It did heal, but it took about 6 months. And fortunately, it never kept me from riding :-)