A big reason for opposition to bike lanes is that, according to the rules of traffic engineering, they lead to car congestion. The metric determining this outcome (known as "level of service") is quite complicated, but its underlying logic is simple: less road space for automobiles means more delay at intersections. Progressive cities have pushed back against this conventional belief—California, in particular, has led the charge against level of service—but it remains an obstacle to bike lanes (and multi-modal streets more broadly) across the country.
But the general wisdom doesn't tell the whole story here. On the contrary, smart street design can eliminate many of the traffic problems anticipated by alternative mode elements like bike lanes. A new report on protected bike lanes released by the New York City Department of Transportation offers a great example of how rider safety can be increased even while car speed is maintained.