37% of workers in Copenhagen commute by bicycle?
One factor is that the city has plenty of well-designed bike lanes. For instance, the lanes are separated from traffic by parked cars, so that "the parked cars protect the cyclists, instead of the cyclists protecting the parked cars."
Of course, another factor is that the cyclists actually stay in the bike lanes and follow the traffic laws, e.g., they all stop at a red light. Fat chance you'd get New York's cyclists to do that.