More fuel for debate.....
As near as I can tell they do not classify semi tractor trailers separately. They show truck with 2 - 3 - 4 - 5 axles etc. A tractor trailer can be 3 axles - steering - drive - trailer - so is classified as a 3 axle truck rather than a truck pulling a trailer. So if you have a dually you could be pulling a 1 or 2 axle trailer and still be classified as a 3 or 4 axle truck by some toll agents. This would be to your advantage if you look at the example I posted above and add things up. Adding a trailer to a dually would be more than if classified as a multi axle truck.
If you are classified as a car or pickup and have a trailer then you could be classified as pulling a trailer and the added rate would apply.
The same goes for those with motorhomes. Do they classify it as a truck or a bus? Does it have 4 axles or is it pulling a car with two axles? If a motorhome pulls a trailer is it a semi or a truck/bus pulling a trailer?
Therefore the inconsistencies. I do not care if you drive some type of pickup or truck or bus or whether you tow a car or a trailer. The answer is the same. Inconsistency either because the toll collector is not sure what to do - or because you are a different road in a different state run by a different company that has different classifications.
We could argue all of this to death. Or we could argue with the toll collector - or the supervisor. Or we can just try to understand that it can vary and perhaps suggest to the collector that we have been charge differently in an attempt to get the lowest rate. We can pay and be on our way without stressing ourselves out over a few pesos. It is quite obvious that different vehicles can be seen differently by different collectors. I do think they rate a dually as a truck and therefore different than a pickup. How they add the trailer could be up for grabs. If in fact they do charge semis as a tractor pulling a trailer than perhaps a dually with a trailer should also be charged the same rate as a semi rather than like a pickup pulling a trailer? I have no idea.