Contrary to what some legal scholars here say, the states can tell the feds to stick the FMCSA regulations up where the sun never shines and regulate the roads as they see fit. (my sources are U of D law school and the USDOT).
The acceptance of the DOT regulations within the states are based on an agreement that was made in the 30's and affirmed in the 40's which the states said they would allow the feds to write most of the regulations for interstate commerce and would abide by them - allowing for a more uniformed regulation. It is an agreement, not a mandate which is very important to understand. What the real problem is the states are not represented in congress by the senate and this is where they can force the states to accept the regulations based on how funding to that state is allocated. Primary seatbelt laws are one example, the feds wanted to make it a regulation that all drivers must use them and told the states they had to enforce it when it was being debated but the states did push back and only a few passed a primary law. This is the same thing, the feds can't enforce the regulation because it is the states' right to do so and the state can say "lahood screw you, we don't care".
