Tony's "Rule 0" was invoked "whenever there was a shortage". It was in
effect for long periods of time when traffic levels were high - but it was
also invoked on a yard-by-yard or even day-by-day basis ... whenever the
clerk "needed" a car. Yes, of course a good car clerk did his best to honor
the rules as much as possible ... it made good sense and saved the
railroad -money- in the long run (usually). But there were many, many
different factors involved in choosing the cars on that one particular
day. And let's not forget that these were pre-computing days (in general).
Why was this true? Because the Car Service Rules were actually more
like "Car Service Guidelines" ... especially when talking about stuff like
"why was this individual car chosen to be used for this particular shipment?".
I am not advocating a practice of just saying "my RR - my rules" ... it is
fun and informative to invoke car service rules on our layouts. That said -
it's not a particularly popular practice to hold some guest yard operator's
feet to the fan just because the car service rules weren't applied rigidly.
A better practice is to reward your YMs who -do- use the rules. *G*