It is I.E. that determines the number of routes to have in place and the number of cars to run. Their decision is heavily based on data history which have been collected for the past few years, and allowances given to each route. Many centers have not had a time study done in quite some time, so this already throws off the figures a bit.
The PAS or Dispatch Sup is the one responsible for making the appropriate add/cuts for each loop. They way loops are setup, the routes furthest away from the center are assigned the first letters in the alphabet, so route 48A is further away from the center than routes 48B, 48C, 48D, 48E etc... The dispatch sup is supposed to make add/cuts starting from the "A" routes, all the way down to the closest route to the center, which in our case we'll say is the "E" route. It is supposed to be a trickle-down effect. In some cases however, that route that is closest to the center gets slammed, but it will be easier to get them help, because they are closest to the center. They can usually also run more stops, because of less time spent driving.
But as we are all aware, this doesn't always work like it's supposed to. For one, the projected volume is consistantly inaccurate. Which means, the center could be lighter than projected, or heavier; usually the latter. But if you are lighter than expected, it just means that volume you were expecting today will be in tomorrow, thus creating a much heavier day than anticipated. As Forest Gump would say, "you never know what you're going to get".
So to compensate, the dispatch sups starts to look at possible add/cuts. If you have an idiot for a dispatch sup, they can ruin your day. Poor add/cuts are worse than simply being overdispatched. One must take into account the milage, number of pieces, traffic for area, pickups, and type of stops, i.e business or reso. Even if he is successful, the preload might forget to physically move the stops from one route to the other.
yeldarb, are you in the Atlanta area?