How would domestic Travel restrictions be implemented?

For example, what would this mean? Would it be people in New York couldn't travel to other states? Or people in Washington State couldn't travel outside of Washington so they would check your license plates and stop you if you had a Washington plate in Oregon or Idaho? If you were from California would you not be allowed in Nevada, Oregon or Arizona or Mexico?

Or would this be county to county and city to city implementation? Not sure how this could work. What if you are traveling and don't have money for a hotel and need to get to where you live to be able to survive the heat or cold? All these things and many more need to be considered before trying to implement anything like this.