Your bracket notation in effect works the same as mine. The difference is that -+- could be any of [-+][--] or [--][+-] by symmetry and so leaving out brackets. In my notation "+" is a character which does not occupy space. Hence [-+][--][-+][--] is the same as -+--+-.
Sorry about the error earlier: "...-+-+-" was a typo that I couldn't edit anymore.
Why are there three characters to represent a pair?
Do you mean something like this:
car with toilet: [+-]
car without toilet: [--]
my pair: [+-][--]
your pair: [-+][--]
?
> This is then the "extra few feet" that he talks of.
Using my notation (sorry to flip it):
[-+][--][-+][--]
That's four cars. If someone is sitting at the right end of car #2, they have an arrow pointing them to car #1 for the toilet. If that toilet is broken, then they must walk back through car #2 all the way to the end of car #3.
But I may be misunderstanding your initial notation.