Both directions of the bike lanes on St-Denis take up about one car lane. The street has 2 lanes for car traffic and 2 more lanes for street parking on most sections of the road. I think that's a fair trade-off for the very high traffic the bike lanes receive on non-snow months. Not all public infrastructure needs to be used at capacity all the time (like public swimming pools, playgrounds, tennis/basketball courts, un-plowed walking paths, etc).

Although Montreal is leading the way to sustainable transportation, I don't think Montreal is copying European cities enough. Most of the biking infrastructure around the city is paint on roads making it a patch work system that kids and elderly people can't use safely.