Forgot to mention - outside of curve shots when shot at track level, one desirable thing is to catch the train much earlier so that the power is not blocking the trailing cars so one gets the entire train. Note how even the second unit here is greatly de-emphasized by being curved away, giving it a strong feel of roster shot.
The following is not the greatest example (a perusal of my shots has just revealed that I don't take many mid-curve shots!) but you can see the cars trailing.
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PhotoID: 176685
Photograph © Janusz Mrozek |