Noticed a lot of dump trucks pulling dump trailers in Washington State. Question: Why is the tongue so long? Seems the length of the tongue is longer than the trailer. Is it to allow easier backing, or to spread out the weight, or what?

So they can Jack knife the trailer and dump the truck over the trailer tongue.

I suspect so he can dump front dump without unhooking, plus turning radius.

Here they can also load the trailer container into the truck and then go dump it, we regularly see truck with doubles be hind it that do that .

there is something called bridge law. has nothing to do with bridges. its the length of the vehicle between axles. to short and your gross vehicle weight is reduced. it does aid in dumping also as was already said