I know #2…Jake Brakes are the loud brakes that some trucks have - here’s how they work. It’s sort of a repeated loud “popping” noise (at least that’s how I hear it). I can see where it would be an annoying sound in a residential area.
Can’t help you on the others.
A bobtail is the tractor of a tractor-trailer unit. (The cab with the really short–or bobbed–back end). Why somone would ban parking of those units (as opposed to banning all 60+ feet of the whole rig), I don’t know.
The kingpin sign would make more sense (to me) if there was a length posted on the sign.
The kingpin is the vertical shaft or pin that locks into the “fifth wheel” on a truck and allows the trailer to turn while being pulled.
A sign warning that trucks longer than x feet, or trailers longer than x feet between the kingpin (where they attach to the tractor) and the rear axle are considered dangerous on a road with narrow, sharp curves makes sense. Without a distance included, I’m not sure that I am using the terms in the same way.
You are correct - now that I recall, it did say that for Trucks/trailers longer than 30 feet. The road (CA hwy 74) is an extremely windy narrow mountain road.