[Mawr]

> cars that require a fraction of stopping distance of a truck at given speed

You may want to update your knowledge on the stopping distances of modern trucks.

> are fined for going 3-4 km over limit

Obviously. Is there anything confusing about the word "limit" in particular that you don't understand?

> Essentially, fined for driving at a speed where they can stop many meters before a truck going the sign posted limit.

It is not your job as a driver to decide whether to stick to a particular traffic rule or not. The limit is there, so follow it.