Re: Positive externality
"We have such a system: it's called fuel duty."
This!!!!! It really pisses me off when people talk about road pricing. We already pay an annual fee for permission to use the roads (VED) then we pay per mile in fuel duty, which generally keeps going up year on year anyway. It even has a self-limiter built in in that if people want to pay less, they drive more efficiently and take a little longer getting there. And not forgetting that the tax we pay on fuel (fuel duty) is itself including in the fuel cost for VAT purposes, ie we get taxed on the tax we pay! Adding tolls or per mile "road pricing" would be a real kick in the balls for all drivers. Every time a politician gets up and talks about road pricing without promising to abolish fuel duty, I just want to punch them in the face!
Also, not forgetting that the vehicles that cause the most wear and tear on the roads are the HGVs who use more fuel and pay more, as well as the idiots doing 80-90 down the motorways who see their own self importance as being more valuable than the 30mpg they are getting. Fuel duty IS per mile road pricing. No special technology or GPS devices needed.