ahhh.. I thought that was at the start and you were clocking in and clocking out.
So that's marking the exit route at a junction? What on earth is stupid about that (even in perfect vis). It's simple and fool proof. I'm a devout believer in not just Murphy's law... but Finagle's law (which I always thought was termed Sod's law, but apparently not??).
It's a hardly complex and expensive system you have there, seems a brilliant idea to me.