LOL, cars don't go anywhere near 25mph in Boston. They'll average 15mph, if they're lucky. Even with ~70% of the right of way allocated to cars, there's still too many of them for the road to handle. I don't know what "efficiency" you think cars have over other modes but I'm not seeing it on my commute. More often than not, my bike is stuck behind cars (because the bike lane disappeared) rather than they're stuck behind me.