For those who know me well, they know I am a huge fan of steam locomotives. And they also know that I am a firm believer that the age of steam locomotives may yet return in a big way.
Why? Well, let's look at some of the facts.
First and foremost, our technology available today would allow for a much more well designed and constructed steam locomotive. Parts will be tighter, stronger, with higher tolerances. All of this would allow for higher steam psi and greater torque, all leading to greater horsepower.
And steam engines, unlike other methods of motive power, have no theoretical top speed. A steam engine's top speed is regulated not by the output of power but the point at which the locomotive will break itself apart.
Second - fuel. I need to do some research, but I have a feeling that burning coal, especially with the air filters and scrubbers we have developed, puts out less harmful gasses than burning gasoline or diesel. The majority of that black smoke you see coming off a coal fire is just harmless carbon, and a good engineer can make a classic steam locomotive put out very little smoke - imagine what a modern locomotive could do.
On top of all of that, the United States is to coal like the middle east is to oil. The United States is sitting on the majority of the world's coal supply, and if the world converted large equipment to being coal fired, the US would become a powerhouse of fuel production.
But even if they didn't use coal, a steam engine can be run on anything that burns or gets hot - coal, oil, natural gas, even nuclear reactions. What do the most techological advanced submarines and battleships run on? What does a Nuclear Reactor use to create electricity? That's right, steam power! A nuclear reactor is nothing more than a big, fancy steam engine. Nuclear material is allowed to react by removing the carbon rods that keep the reactions in check, which in turn generates a lot of heat. This heat is then transfered to water which turns to steam, spins a turbine, which in turn creates electricity.
And the other ingrediant to run a steam engine, water, is the most abundant substance on the planet, and running it in a steam engine does not consume it (turned into something else or tainted (read sewage)), it just gets heated up and moved around. And towards the end of the steam era, condensers were starting to be developed that allowed a steam engine to reclaim most of the water it used.
Yes, I firmly believe that we will see steam engines on the rails again in a big way. I have seen the future, and it is the past.