On those heavy hauls it's all calculated out for legal axle weights. And stopping power is increased by brakes on main axles and engine brakes on the tractors plus they rarely get over 45 mph.
I used to haul CAT scrapers with a four axle tractor and three axle lo boy at freeway speeds, set the Jake Brake on high and had control at all times no matter the grade.
2016 RAM 1500 - 2016 Keystone Laredo 265SRK
The road goes on forever and the party never ends.