The Reason Why Are Trucks Getting Bigger

An idea for a regulation would be to measure the ratio of maximum weight of living things that a vehicle can transport / weight of vehicle when empty, and make this ratio grow progressively bigger.

The ratio is probably around 0.1 today on average (just an intuition, I don't have the actual numbers), and ideally it should be close to 1, or maybe over 1.

For an ebike for example, it's around 3.

Moving 2-5 tons of metal to transport just one human being is positively insane.

My car can happily seat 4 adults (so let’s say 250kg) and weighs a touch over 1000kg, so the ratio is 0.25. 0.1 would mean that a car that seats just 4 adults weighs 2.5 tonnes, which seems extreme?

The average weight of a mid-sized sedan is about 1,500kg, and the average weight of all American cars is closer to 1,900kg. A 4-seater close to 1,000kg is exceptionally light by modern standards. The Mazda MX-5 is a 2-seater which is famous for being lightweight, and it also weighs a few kg above a ton.

Also going off maximum human capacity isn't great in context, as the average car journey has <1.5 occupants. Not to mention if this was codified, car manufacturers would simply put folding seats in the trunk.