“It’s called the Manual on Uniform Traffic Control Devices (“uniform” italicized to emphasize uniformity — that a thing is consistent, the same), issued by the U.S. Department of Transportation to “… establish national standards for all traffic control devices, including road markings, highway signs and traffic signals.”
This is worse than the mere “variable speed limit” issue. Worse because (using federal purse strings on “federal transportation funds”) it interjects FEDERAL LAW into areas of transportation where any federal ruling is not just unnecessary but an unwarranted extension of federal power.
The “variable speed limit” issue can tested in the courts, but getting the federal government OUT of the business of “setting standards” where no “national standard” is needed will require a Congress elected to deconstruct the Liberal/Progressive deep state and its tentacles into EVERYTHING.
You can’t have it both ways. If the Federal government has no legitimate constitutional authority to regulate interstate highways, then states have no business holding their hands out, begging for Federal matching funds for major highway projects on the grounds that they are assets of national importance.