A locomotive seen in the time stream.
A locomotive is a self-propelled vehicle, usually electric or diesel-powered, for pulling or pushing freight or passenger cars on railroad tracks.
After Jonathan Archer restored a damaged timeline, a locomotive could be seen in the time stream as the timeline realigned itself. (ENT: "Storm Front, Part II")
Beverly Crusher's holodeck simulation of the Orient Express featured the locomotive, along with the rest of the train. (TNG: "Emergence")