Who sets traffic rules on the Interstate System?
Because the States own and operate the Interstates, the States establish the operating requirements, such as speed limits. The States also are responsible for enforcement.
The National Committee on Uniform Traffic Laws and Ordinances (NCUTLO), which includes State motor vehicle administrators and police officers, publishes a compendium of model traffic laws and rules of the road. The goal of NCUTLO is to promote uniformity across the States, but each State is free to adopt its own traffic laws and rules based on its unique circumstances.
There are more citations on that site making it clear the States establish the rules for Interstates.
The law cited earlier is on point.
Look. I really don’t care. The feds front the money and make the rules. The interstate is the one of the remnants of the cold war. They were built to move armies quickly. It may seem like it is the state that owns and sets the rules, but it isn’t. Perhaps the feds gave the whole system over at one time and I missed that meeting, but when the feds want it back, they’ll take it.
All I know is that every state I have cowboyed in you do not drive cattle onto the on ramp, down the interstate, or across the interstate, except under special permit, not just because it isn’t safe but because it isn’t allowed.