I find the topic interesting. It is not a make or break issue travelling to Mexico. Every time we count out the pesos for the toll we are invariably wrong.
We are not a pick-up or dual wheel pick up, but we do have dual rear wheels and a tag plus a tow car. We have found we are classified as a dump truck and car, a bus and a car, a semi truck.
Sometimes I think the car is a surprise after they have already punched in something, don't know.
I think it would be helpful to post a picture of the different classifications as seen approaching the toll both.This may allow others reading to get a better idea of what the post is all about.
Oddly enough, we have paid tolls in the US and have never had to wonder after reading the sign, what we were charged for or how many axles.