This is correct, there is no legal mechanism to restrict travel as it is a constitutionally protected right, like free speech. In fact, the US Supreme Court has

This is correct, there is no legal mechanism to restrict travel as it is a constitutionally protected right, like free speech. In fact, the US Supreme Court has ruled that it is illegal for the government to enact de facto restrictions on common means of travel via regulatory powers e.g. closing all the roads. Restrictions on use of means of travel are allowable for narrow, limited purposes, like when the FAA grounds aircraft due to imminent safety issues pertaining to their operation (e.g. 9/11 or design defects). Like with all fundamentally recognized rights in the US, there are no exceptions for broad emergencies, and the Supreme Court has consistently upheld this view in modern history. Abrogation of fundamental rights can only be done in very narrowly targeted ways and generally comes with a due process requirement.