Definition:
A transition car is a tool used by modelers when converting from one type of coupler to another. Placing an old coupler in one end and a new coupler in the other allows the car to be slipped in the middle of a train to transition between the two. By using cars like this, you can convert a large fleet at your own pace without leaving cars on the shelf.
For example, a car may have a horn hook coupler on one end and a traditional knuckle coupler on the other. Eventually, enough of your roster will be converted that the transition cars can be completely switched over as well.
With an increasing number of models coming with automatic knuckle couplers in every scale, the use of transition cars is diminishing.
