There is one of these for every operational car in inventory. When the car is loaded a waybill will be place here to direct the routing of the car to the proper destination. When the car is MT it will either have an MT request place here or if no MT request exists the car will route back to its default MT location denoted by the header. In this case the default MT location is White Hall yard.
These two documents the waybill on the left and the empty (MT) request on the right in addition to the Car Card are the only car movement controlling documents.
Every waybill that does not have a corresponding MT car at the business or in the same town will have an MT request placed at White Hall yard (purple cards in the above picture) to instruct the yardmaster to locate and route an MT car to this business.
There is one of these for every business located on the layout. Whenever a business generates a waybill it is placed in here behind any other waybills that might be waiting for MT cars. The waybills are then loaded into Car Cards from front to back.