Bumpy, the "Braking Performance Standards" are ALREADY in the Federal Motor Vehicle Safety Standards (FMVSS). Most state laws simply mirror the FMVSS.
CA does not. They allow 5 feet further than FMVSS. MT is practically word-for-word, as are many other states. The Standard specifies that the test is to be done on a level, clean, dry, hard surface. It does not specify what the surface is to be made of. See MCA 61-9-312 to find the exact wording.
If a LEO writes a ticket for failing to meet the standard, it is HIS responsibility to show the ticket is for a valid infraction, it is not the driver's responsibility to prove the ticket is wrong. If the LEO can not accurately perform the necessary test, he will not write the ticket.
Does that mean the Braking Performance Standard is rarely enforced, and for all practical purposes is unenforceable?
Yes, I guess it does!