Give me the DOT link then

Also, as I said, the three lights are not at the top for every truck, therefore, it is not for height indicator.
Swing and emergency brake will cause worst situation and involve more car crashes. I have seen a TV program several years ago in US that ask people just reduce speed and crash into deers, without swing, under emergency. For trucks, the most possibility is that a small car cut into the truck way and give a sudden stop. I agree nobody wants to crash into front car, but that will give less chance of injury to truck drivers and cars around the truck.