Look harder still... at about 0:15 or 0:16, if you look at the road along the left trolley rail, you can see some missing asphalt along the rail a couple of feet before where the bike landed. Likely a combination of two. When he reacted and got on the brakes HARD, his front tire also got trapped in this missing asphalt. If you look close at the video you can that his bike is pretty much lined up with that left trolley rail. I wish I knew how to do a screen grab from youtube... I'd post it up. Edit: Also visible near the orange shoe at around :051.