There are three styles of trains that most people will run into, or atleast used too. The Steam, Diesel and Electric trains. Each one is as diverse as any car, and have been around for over a century. They are what lead the evolution of the world from agrarian into an industrial nation.
The Steam Locomotive was the first generation of locomotive. Powered by water boiling and pushing pistons, it was used from the 1800′s all the way to the first part of the 1900′s. Even then they were only phased out when they were too hard to maintain. The largest locomotive ever built was the was the 4000-class built for the Union Pacific. It was nick named “The Big Boy“. (not actual locomotive below)
Up next was the Diesel Locomotives. They could produce the same power as a Steam Locomotive in a smaller package. These also could pull more and were far more economical. They are still used all over the world from logging railroads to interurban. Almost every railroad in the country uses Diesel Locomotives in some form. There is alot of new technology developed on diesel engines that eventually trickle down to the auto industry.
Of the three, the most economical is the Electric Locomotive. They run by either overhead or third rail. These are most common in urban environments. They can be large locomotives pulling freight or a Trolley. Trolleys were very prevalent in the early 19th Century in many cities, but were slowly removed for bus services. But some cities still have “light rail” which uses electricity as their power source.