Part 3: Certain other federal powers are forbidden the States except with the consent of Congress: No State shall, without the consent of Congress, lay any duty on tonnage.
Laws which limit the overall weight of trucks prevent the installation of safety equipment such as disc brakes and roll-over protection. It is not that brake rotors weigh more than brake drums, but the mechanical structure necessary to hold the brake shoes on the outside of the rotor is considerably more massive than the axle end fitting that holds the brake shoes inside a brake drum. A truck with disc brakes is likely to get $1,000 a week in fines. Even carrying a pair of 30 lb. fire extinguishers could result in a $60 fine under the present law.
A law limiting cargo weight to 20 metric tons (44,080 lbs.) would not affect the overall weight of present trucks, but it would allow the development of new technology such as regenerative braking in which heavy batteries are used to store energy during braking. See the Safety truck. The reason for preferring metric tons is that many foreign shippers do not understand English weights and measures. Overweight shipping containers from overseas is a constant problem.
A law deregulating the overall size of trucks would not result in 100 foot long vehicles since the size of the cargo compartment would still be regulated. The width of the cargo container should be regulated because it determines the visibility to the rear through the mirrors. Deregulating the width of the trucks would allow the cargo to sit between the wheels rather than on top of them. This would improve visibility to the rear by resulting in a shorter one-unit vehicle with less distance between the mirrors and the back of the truck. A single-unit vehicle (without a trailer) could also be equipped with a video system for improved visibility to the rear.