With some inexpensive hardware you can build a simple motion control system for your time-lapse work.
The interface between the computer and the locomotive uses two inexpensive Phidget devices.
You can get these parts directly from Phidget...
Phidget Interface Kit 2/2/2
http://www.phidgets.com/products.php?product_id=1011
Phidget SSR Relay Board
http://www.phidgets.com/products.php?category=9&product_id=3052_1