Oh My,
Someone is complaining about the same issue I have been annoyed by for many years.
In our case, we have an antique coach that happens to have a rear axle (One Axle by SAE definition) but it is tandem (one in front of the other) instead of dual (tires side by side). So, many places charge us with the 9500# 23' coach the same fare as full sized Greyhound. If they could go so far as to actually count tires, that might be nice (we only have six), or actually charge by weight (we would do well on that too), then I might not feel so cheated. But as a friend of my daughter's said (with a straight face),"You have a motorhome, you must be rich enough that you can afford any tolls they think can think are appropriate."
This is why we have maps and toll charts. We can afford to drive quite a long ways to avoid an exorbitant toll. We get to see a lot of nice country that way.
"Thanks to the Interstate Highway System, it is now possible to travel across the country from coast to coast without seeing anything." - Charles Kuralt
Matt