A shuttle train is a train that runs back and forth over a short route. Shuttle trains are used in various ways in different parts of the world. They can be used to carry passengers, freight, or both.
Aichi Loop Line shuttle train at Mikawa-Toyota Station, Toyota, Aichi Prefecture, Japan
The "2007 Holiday Shopper's Special", which ran on December Sundays, is a train of museum subway cars. This particular car is displaying the (former) S Special on its rollsign at the 23rd Street (Sixth Avenue) station.