[mpapi]

They're not exactly common in the Boston area, but they're here, and new ones are getting added (mainly in Cambridge, as far as I can tell). At least one even has separate traffic lights that turn green for bikes a few seconds early.

FWIW I tend to stick to the roads anyway, though, because the segregated bike lanes often have pedestrians and runners in them regardless, and the paths often get cracked from tree roots and whatnot. Most drivers don't seem to care if I'm not on the dedicated path, so long as I'm hauling and not riding crazy.