while we're at it, let's make the congestion pricing proportional to some power of vehicle weight so that it also reflects the cost of road maintenance.
Drivers pay fuel taxes already. Fuel taxes are proportional to vehicle weight and power.
IMHO, it better to tax normalized_areanormalized_weightnormalized_congestion . For example, if vehicle is 30% spacer than average, has 50% more weight per space than average, and uses road at peak hour when road usage is 50% more than average, then it should pay 1.3 x 1.5 x 1.5 = ~3x tax. If owner want to reduce tax, then it should use smaller, lighter car, and use it at off-peak hours, e.g. 0.9 x 0.9 x 0.5 = 0.4.
I mean, are they really proportional to weight and power? My Cayman weighs less than 3000 lbs, uses very little of it's power, in traffic, and gets 12-16 mpg (around 30 in no traffic). My rx300 weighed nearly 4000 lbs and would get 21-23 mpg in no traffic. My rx300 saw almost no traffic whereas my Cayman sees a lot simply because my last job didn't care whether or not I came into work (unless there was a meeting I needed to go to).
To top it off with more extreme anecdata, our Mercedes Sprinter-based RV gets 15 mpg, similar to your Cayman, but fully-loaded it weighs 11,000 lbs. (source: truck stop scale).
Weight or axles, but fuel tax isn't the way to do this. I'll leave it as an exercise for the reader to come up with the sedan MPG necessary to beat a 40,000 lbs. semi that gets, say, 3 MPG. (And, BTW, semis haven't done as poorly as 3mpg for a long time.)
the poster you are replying to misunderstood my sentence. there's no reason to directly tax powerful vehicles, unless you are using it as a weird proxy for fuel efficiency, which is already captured by per gallon fuel taxes.
I'm saying we should tax vehicles in proportion to some integer power of vehicle weight, since the road damage is superlinear with respect to vehicle weight. a big truck that weighs ten times as your Cayman does much more than ten times the damage. since we're trying to fairly distribute the costs of transit, the operators of these vehicles should be paying the lion's share of maintenance costs.
