My process to restage cars in staging by finding a role for each car relies on being able to find at least one suitable role for each car that is restaged. If no role can be found the car must be removed temporarily to storage. This approach works well when there are enough suitable roles to select from for a given car, but it breaks down when there are not. Too many cars may end up in storage when the entire point of the exercise is to run trains! A solution to keep cars moving is to substitute roles that are not a perfect match and carry on. Colin mentioned that he and Gary often have to do just that when using their traditional paper car card and waybill system. I’d like to capture some of the ideas behind how this “forced” matching is worked out and implement it in the program.
There are obvious things we can do in some cases. For example, if the particular car to be restaged has 6 foot doors but there are no roles asking for a 6 foot door, only 8 foot, then we may decide to send the car anyway, even though its door is narrower than what is requested and a real shipper would be angry because their forklift truck would not fit. The basic notion here is that there may be some parts of the car spec that can get ignored to help find a match, without causing too much grief. In this case we ignored the door attribute because it really doesn’t matter, nothing will actually be loaded. Maybe there is an order of things that we can ignore in the hope of finding a match so that the car does not have to get pulled off into storage. For example, if we don’t find a match to start, first ignore the door spec, if still no match, then ignore the car class, and so on until we run out of things we are willing to compromise on and the car has to be moved to storage. I suspect that people go through something like this in their minds when selecting paper waybills. I’d like to try to capture that in some simple rules that I can implement in the program.