Wikipedia
The expression shuttle train refers to a train that runs back and forth between two points, especially if it offers a frequent service over a short route. Shuttle trains are used in various ways, in various parts of the world. They commonly operate as a fixed consist, and run non-stop between their termini. They can be used to carry passengers, freight, or both.
Usage examples of "shuttle train".
Overhead, another shuttle train hummed almost silently along its guidepath, bright against the brown-toned glass that formed the building’.
I made it to the shuttle train, having successfully avoided the blandishments of a thousand hucksters selling everything from inflatable Neil dolls to talking souvenir pencil sharpeners to put a point on your souvenir pencils.
The shuttle train hauled my mollusk-stuffed carcass over to Times Square where I caught an uptown BMT local to 57th Street.
And if, on changing over to the East Side line to get down to Canal Street he materialized a second time, in the closer confinement of the shuttle train, my quarantine of all danger within Mordaunt's house made this nothing, made it just a coincidence.