I might have worded the last post wrong I was saying the states can increase the standards or toughness of a law. but not decrease it.
That's not correct, necessarily, depending on your point of view, or which way is considered toughening it. In this case, the STAA was enacted to standardize weight & length laws.
Before the STAA, things were really crazy. Imagine the patchwork of laws we have now, then apply it to size & weight. As Mona Lisa Vito put it, "WHAT A F$@&!!& NIGHTMARE!" So finally the feds wised up and used the powers available to them under the interstate commerce clause, and standardized them on the national network. On roadways other than the national network, local laws still apply. On the national network, the feds say, state & local governments must allow
at least 13'6" in height and 80,000 lbs. They can allow more, but the STAA eases our lives by mandating
at least that.