The Ultimate Steam Page

Steam vs. Diesel-electric

Diesel-electric locomotives had several advantages over steam locomotives including:

(1) "mutiple-unit" capability, allowing several diesels to be connected together and controlled by a single operator
(2) very high starting tractive effort relative to their weight
(3) use of light oil fuel which provided much cleaner operation
(4) use of mass-produced, standardized repair parts simplifying maintenance and repair procedures
(5) extensive "factory support" in the form of extensive operating and maintenance manuals, training, etc
(6) significantly higher thermal efficiency (~25% at the rail typical for diesel-electric; 7% at the rail typical for "modern" steam).
(7) higher availability (less time spent on routine repairs and maintenance)

Of course, steam has significant advantages too:

(1) High horsepower-to-weight ratio
(2) Allowed very high horsepower in a single locomotive
(3) Much lower first cost per horsepower
(4) Relatively simple to repair
(5) Use of cheap, unrefined fuel (coal, wood, or heavy oil)

Steam designers from the 1940's until the present day have sought to minimize the disadvantages of steam while maximizing the advantages steam did have over diesel-electrics.