Nice exposition by Felix Salmon on traffic. Since people get used to paying tolls, car licensing fees, etc., the idea is that to get people to pay attention to a fee enough to change their behavior, it has to hurt just a little more than usual. So to make "congestion fees" actually work, leaving easily jammed places comparatively free of traffic, the fee needs to be constantly shifting, not just another cost of daily driving. Since it's basically designed to annoy, it annoys people, and has a tough time becoming law. Too bad, since they do work!