I don't know if this excuse holds water. If 28 disparate states with different freight profiles can pull it off, surely the US can too.
It's all about will.
It's all about will.
The span under the trailer behind the rear drive axle(s) and the forward trailer axle is much longer than you find on European trucks. That means you need a much longer underride guard. You also have to convince trucking company execs that all that extra weight is a good thing even though they know it's cheaper to pay the occasional settlement after a gruesome accident.
Also, putting the trailer axles further forward to shorten the gap is not possible until Indiana changes their minimum axle length regulation (40 feet trailer kingpin to rear axle centerline) because I believe that while they are the only state to have such a rule, you can't do much interstate commerce with a fleet of trucks and avoid travelling through that state with its central location.
Trucking in the US is massively regulated and bureaucratic and you are going to need a lot more than will to get it to change. I'd love to see safer trucks too but I am not optimistic about seeing underride guards in the US anytime soon.
You're only touching axle weight and distance, but I wonder if the max length (truck + trailer) is clearly defined? Are you allowed to have more than one trailer (here: Nope unless you're driving a tractor most likely)?
I have a BCE ('40 tonnes', biggest you can get here) license, although it is currently inactive¹. Trucks continue to amaze me and I'd like to understand how different the world is over there.
①: Truck licenses have a renewal date here in DE. For people far above my age (my dad) it's something like "Every five years after you're 60" or something like that. For me it was "Every 5 years" from the get go and I haven't renewed it for quite some time. I still could get it back, but would need to visit a doctor (general health), optometrist (field of view test) and maybe redo a first aid course.