Over on cyclelicious blog there is a nice explanation for the rules used to estimate the damage done to road surfaces by vehicles. This is often the hard numbers appeal for making cyclists pay for the infrastructure they use.
It would be a fair argument providing that principle was applied to ALL road users.
The crowning achievement of the cyclicious article is its ability to translate the $4 bicycle tax in Colorado Springs into its automotive equivalent. If you apply the 4th power rule applied to the estimation of vehicle damage, and if you scale the tax up to the size of a vehicle like the Prius, you’ll be forced to ask drivers to pay $154,000 in tax.
I’m serious the gap between the damage a bicycle does and a small compact car is that significant. I highly recommend reading the article – it spells out the equations used by traffic planners more fully.