Train operation in severe winter weather - Trains Magazine

What I learned when I studied the Carnot cycle, Erik, is that  the high temperature and the low temperature set the limits and efficiency is possible only between these limits.  By operating in winter the distance between the limits increases and in theory the efficiency of a steam locomotive increases.  

I also learned that thermodynamic principles were not used to design steam locomotives.  Design principles emerged from trial and error.  Thermodynamics came along after the engines had been designed.  

Finally, I understand that condensing steam locomotives are not generally used except under special conditions such as in deserts where water is scarce.  

John