when I was a teenager, I intended on pretending I was driving a train from Los Angeles to New York. I figured out how many scale miles it was around the loop of my 4x8, and how many rail miles it was coast-to-coast. I can't remember how many laps I figured it would take around my layout, but the number was HUGE. I think I made it less than 50 scale miles before I got tired of counting!
In HO scale, old athearn blue boxes can make it a long way with only minimal sevicing. I've heard old steamers with cast frames (Mantua, Varney, Bowser) can make it quite a few miles. I remember a model railroader article where a museum had a civil war train exhibit, and it said the museum had found the Mantua general to be most durable.
I don't know who makes the most durable locomotives in N-scale.
Kevin
