This motivated me to look up the Philly Municipal Code. It now requires a "brake." At one point in time it did not specifically use the word "brake." Instead, it required something like a "mechanical system" capable of causing a skid within a certain number of feet. I believe there were some other jurisdictions with similar language and once read something about someone arguing that the legs of a fixe rider qualified as a "mechanical system" under the law. I'll bet that potential argument was the impetus for the change.