This means to move the camera left to
right (if the train is arriving from your left), keeping the engine in
the view finder as it passes. This means very little movement of
the engine compared to trying to shoot from a fixed spot as the train
moves by. The only movement showing in your still picture
will be the foreground and background, which is a good thing, it proves
the train was not sitting still on the track.
Rather than risk getting a good shot on
one panned exposure, set your
camera for multiple shots (sometimes called a burst of 3 or more
exposures) as the train passes, then select the best one.
This is an
application of panning. However, the sun was so bright on this
winter morning and the sky so clear, there is nothing blurred.
The direction of the steam indicates the train was moving. One
thing about trains and the fact that they are on tracks, the engineer
doesn't always have to watch where he is going!