No, not just tractor trailers. Straight trucks also use weigh stations. Even those guys with pickups towing travel trailers from manufacturers to dealers are required to cross weigh scales. Anything involved in commercial hauling has to cross a scale unless told to bypass. Even a farmer with a dually pickup and a gooseneck livestock trailer. All of these, because of being commercial uses, fall under Federal Motor Carrier or State DOT guidelines. Tough to consider the 1/2 or 3/4 ton pickup that is used to commute to work and haul a lawn mower to repair shop a "truck".
No, in many locations, "trucks" are required to stay out of the left lane of travel. St. louis, Chicago, Kanas City, LA, ad nauseam. And in many locations, they are required to operate at lower speeds than cars/pickups. And in just about all locations, simple infractions carry a larger fine and more penalties than driving a car or pickup. Has absolutely nothing to do with being a semi truck and trailer. It is set by states based on weight, number of axles, etc. For instance, some states say vehicle with more than 6 tires. Some if the empty weight is over 4 tons. Some if there is more than 2 axles.