I am not positive, but I think Mechanical Engineer.

"Mechanical engineering is the discipline that applies engineering, physics, engineering mathematics, and materials science principles to design, analyze, manufacture, and maintain mechanical systems. It is one of the oldest and broadest of the engineering disciplines. " https://en.wikipedia.org/wiki/Mechanical_engineering

My father was one, but designed gas compressors for oil & gas industry.

I'd go with SapporoChris's answer with Mechanical Engineer.

Locomotive Engineer's basically are the one in charge of operating the locomotive. What most people think of as a "Conductor" is actually a lower level job and is mostly paper work from what I hear.

Source: Close friend is a Locomotive Engineer in Canada.

We call them train drivers in the UK. I think it's a bit too muchbto call them engineers...

Well, another term for a locomotive is an engine, a train engine. So a person who works on those is an engine-eer.