I like to use a red filter only when the skies warrant it, much less attention being paid to the rolling stock. In fact, the train then often becomes the second point of interest, with the atmosphere and location holding the limelight, so to speak. I would use a red filter for dramatics, more than anything. As mentioned, the red increase the contrast considerably, and I ususally find it requires a full two stops of correction. A red filter is very limited in practicality, in my opinion, and as mentioned might lend a little IR feel to an otherwise dull, flat scene.

My photography easily shifts from stock-solid action and roster shots with great lighting and color (which, in itself is actually more difficult to capture than not!) to something a little more moody. On a cloudy, overcast day, I don't stop taking pictures, but I usually concede that that shiny clean paint job rolling by me just ain't gonna happen with color slide film today! So, I shift to B&W, with its suggestive powers, and either raise or lower the contrast to suit my own desires.