That hasn't been my experience at all (living in the DC suburbs).
Local example: I live in Reston VA. We've slowly been adding bike lanes to existing roads as other improvements are made. In some cases, this required cutting from 2 lanes to 1 lane. However, in all cases, traffic timings and accident analysis was undertaken and in all cases that I've seen, traffic flow either improved or if there was a decrease, it was on the order of 1-2 seconds per mile traveled. Additionally, in most cases, traffic accidents of all kinds were reduced.
But, you wouldn't know it from listening to the anti-bike crowd. They see the reduction in lane count and immediately jump to "nobody rides bikes!", "run them over" or worse. Seriously, it's that bad.
I'll also add that in some places, the bike lanes are rarely used, but that's as as direct result of poor designs created to silence the noisy motorists. Another local example - the main thoroughfare along my neighborhood has bike lanes. However, the lanes stop just prior to the two places you would want to ride your bike - the high school and the shopping center. So, of course fewer people use the lanes - they don't actually GO anywhere! It's infuriating.
Edit - the sidewalks along this same thoroughfare also start/stop or switch sides. This makes it less tenable to walk to the school or shopping (the road is about 2 miles end-to-end; shopping center at one end, high school near mid-point). Lots of people are within 1 mile of either destination, but running back and forth across a 45mph busy road is simply unsafe. A pedestrian was killed a year ago running from the sidewalk on one side to his home on the other. How the heck is this even to code? Argh.