The states do have the authority to regulate commercial activity but as you will see most of the people they are stopping are not engaged in commerce.
If you research the history of the "drivers license" you will find out they were issued to people who were engaged in COMMERCE.
Meaning, the only people that were to attain a "drivers license" were people who were "driving" using their vehicles to make money in the state. For instance, taxi cab drivers.
These inspection stations started around the 1920's under the guise of keeping your food safe but really it was just another control mechanism.
I'm not saying no good came from them...I'm just saying that it was a means to control the flow of goods rather than keeping your food safe.
Incrementally as they gained the people trust is slowly got out of control. You don't boil the frog all at once you slowly turn up the heat.
"...For while a citizen has the right to travel upon the public highways and to transport his property thereon, that right does not extend to the use of the highways...as a place for "private gain." For the latter purpose, no person has a vested right to use the highways of this state, but it is a privilege...which the (state) may grant or withhold at its discretion..." State v. Johnson, 245 P 1073.
"The right of the citizen to travel upon the public highways and to transport his property thereon, either by carriage or by automobile, is not a mere privilege which a city may prohibit or permit at will, but a common right which he has under the right to life, liberty, and the pursuit of happiness."- Thompson v Smith, 154 SE 579.
"The right to "travel" is part of the Liberty of which the citizen cannot be deprived without due process of law under the Fifth Amendment." Kent v. Dulles 357 U.S. 116, 125. Reaffirmed in Zemel v. Rusk 33 US 1.
“The right to travel is a well-established common right that does NOT owe its existence to the federal government. It is recognized by the courts as a natural right.” Schactman v. Dulles