just saw the movie a couple of days ago, aside from the obvious dangers you can see on the movie, like lots of cars and intersections, where in reality, by the way, there is no time to figure out all your options to avoid a crash, normaly you get one chance to be on the safe side, there is also a learning curve to ride a fixed gear bike. What we dont see in the movie are crashes provoked by the actual crankset, if you come from a normal bike riding formation then you are used to coast from time to time, if you do that on the fixed gear you will surely fall, back wheel jumping like in rodeo, what we see on the movie is not easy, when Wilee stops the pedals and the bike brakes against the tarmac, there are skills involved in doing that,