I believe the idea that steam was more expensive to maintain was shot down in HF Brown's dieselization study in the 1960's. Maintenance costs actually went up during dieselization. If I remember correctly, most railroad folks were comparing 40 years old steam with the new diesels and using that as the basis for the myth. Brown corrected for this by comparing the maintenance costs of the newest steam engines circa 1940's (less than 10 years old) with the maintenance costs of similarly aged diesels and found that the diesels of similar age had higher maintenance costs.

I think the misperception lies in the fact that the reciprocating parts of the steam locomotive are well in sight, whereas the reciprocating parts of the diesel (not to mention wiring et al) are hidden behind the sheet metal. But the bigger expenses of diesels (and somewhat of a suprise to Brown from what I read on a different forum) was in the cost of lubrication - higher for diesels than for reciprocating steam.

That being said, it pays to remember the KISS principle from college - the simpler something is the cheaper it is (or something to that effect). A reciprocating steam locomotive is actually a very simple machine, less complicated than diesel-electrics. Even with modernization to match EPA requirements for coal combustion and increases in thermal efficiency, an external combustion engine is so much simpler than a compression ignition engine, and the subsequent application of that energy into motion via reciprocating steam is simpler than that required to turn those traction motors on the diesels.

Of course, electric locomotives have a very good track record of low maintenance costs. However, that savings is overcome by the cost of constructing and maintaining the catenary/substations/ etc.

I agree with Ernest Robl that if US railroads were to build long(er) tunnels to eliminate certain mountain lines, electrification may be a requirement for operations through those tunnels (especially if they are on a grade), not just an alternative motive power source. My solution to long graded tunnels is to construct them as two separate unidirectional drift tunnels. With drift tunnels you don't have to worry about having to work the engine hard to get through a pass regardless of which direction you're going, ideal for steam or diesel. Of course, until someone does a comparative analysis of the cost of constructing either an electrified line with a single long tunnel or two unidirectional tunnels for conventional motive power operation...........