The "po-po" can also be said to enforce "some interpretation" of federal immigration laws, federal tax laws, and federal labor standards laws too. Your statement is vague and lacks foundation. My point has already been confirmed by your own citations of:
S5.8.10 Unless otherwise specified in this standard, each lamp,
reflective device, or item of associated equipment to which paragraph
S5.8.1 applies may be labeled with the symbol DOT, which shall
constitute a certification that it conforms to applicable Federal motor
vehicle safety standards.
Perhaps "interpretation" was a poor choice of verbage.
Yes, I said I was wrong regarding the markings of DOT/SAE approved lighting... the federal standards do not require the markings, though some states still may.
FMVSS - DOT is not an enforceable standard by anyone other than Federal or State appointed safety inspectors, and the courts. We do not have mandatory safety inspections here in California, only SMOG. It might be possible for the cops to send you to one of those inspectors, its called a fix-it ticket.
Each state either follows the FMVSS code or has their own modified version of it, based off of the FMVSS codes. So, yes, you can say that the FMVSS standards are not enforceable by police officers, because it is a federal standard. However, the state standards, which are the same as, or are based upon, the FMVSS standards are certainly enforceable by law enforcement officers... even if only to a certain degree.
It doesn't take a doctorate in engineering to determine that a set of brake lights that are 10" off the ground are illegal or that there are no reflectors on the back of your bike or you don't have any license plate illumination... direct violations of said vehicle code (Federal and California), black and white.
Where your circumvention of the law methods may work are in the details of the codes... like a replacement taillight that is not DOT approved (also violating state code)... it still functions the same as the original, approved part, but does not meet the photometric standards for an approved replacement unit. There would be no way for a police officer to determine photometric performance of that light, so you may get away with it as it is a bit gray. The same would apply to a license plate light if there was one, but maybe not bright enough. As you said, you may end up with a fix-it ticket in these hypothetical situations, which would most likely result in requiring remedying the offending item(s).
So, I would say the vehicle safety standards are enforceable by an officer of the law, though, not all of the details of the standards, especially where a testing/performance requirement is involved.
