Here we have a video of the biggest trucks in the world, used to carry three times the cargo that a normal truck could carry or pull. There is no explanation if these trucks are allowed to be driven in all highways, but for sure on some they are not.
This is because they are too big and too heavy for the normal asphalt that the streets are made of, so there is a chance that they will make bumps on it, and disturb the ongoing traffic there. The largest trucks in the world are made and are used by companies that are authorized by the government to do so, because not everybody can make and drive these large trucks.
They are used to transport special cargo, in special circumstances and the police needs to be aware of the transport too, to clear the traffic and the road for the large truck. Sometimes there are airplane parts that are carried with these trucks, when the parts are sent overseas.
The engineering skills needed to build such trucks should be on highest level, but you have to be hell of a driver too, because not everyone gets to drive them.