Anytime we get all romantic and think of moving to London, please remind us that the winters are cold, the sinks are stupid and the congestion tax is high. And it may get even higher for drivers of lower-mileage vehicles. Mayor Ken Livingstone has proposed a charge leveled at SUVs that would cost drivers 25 quid a day to drive in London's downtown zone, based on a scale that would give breaks to low-emissions vehicles. What's interesting to us is that the story talks about two different criteria; the amount of carbon released into the air and a vehicle's mileage. Those two info models may often correlate, but they're not necessarily one and the same. So which is it?