They should pass a law that the yellow cars have to take the route I made for them to bypass the red cars. Or put up some signs, "Red Cars Only Beyond This Point".
I can always count on people to decide on lock combinations by arbitrarily choosing whatever they happen to see around them. Otherwise, I would still be stuck in dozens of locations.
I think Level 9 might need another proposition to make it a purely logical, non-semantic argument. For example, that
IF I wonder if that's a relevant clue,
THEN the machine thinks that that's a relevant clue.
For all x, IF x is a red herring, THEN x is not a relevant clue.