I wouldn't say they're widespread in Europe, but I moved from the SF Bay Area to Copenhagen, and they're certainly a big factor here. The "bicycle highways", completely separated and wide lanes that form major arteries through the city, make it much easier to bike to work from most places, without danger of car interference, or of being "doored" by parked cars opening their doors.

Some other efforts: 1) the traffic lights on several major arteries have been synchronized to typical bike speeds, rather than car speeds, so in good circumstances you can ride their whole length without hitting a red light (they call this a "green wave"), and 2) of the three bridges over the central harbor, one is bicycle/pedestrian-only (http://en.wikipedia.org/wiki/Bryggebroen), with another no-car bridge under construction.

Obviously other aspects also matter, such as a compact and flat city, but I think all these help considerably as well.