What are truck weight stations for along the highway?

Not an expert, but I believe that permits have to be issued for trucks moving across state lines (and maybe other things), and the permits are based on weight.

Also, there is a maximum weight limit for highways, too much weight creates large forces on the roads, the weigh stations are there to make sure that trucks do not go above the limit.

Based on the size of the truck, its number of wheels, etc., it is only safe for that truck to carry so much weight. If a carrier tries to overload his truck to get more cargo to another site, it will show up at the truck weigh scale, and the trucker (or his company) will be fined and have to unload a certain amount of weight.

The actual reason is to ensure trucks aren’t carrying unregulated cargo. Truckers are required to keep logs of what they’re shipping and its route. Weigh Stations make sure OTR truckers aren’t picking up extra loads on the sly, sometimes contraband.