At the end of 1949 it is estimated that on the nation's Class I railroads two thirds of the motive power was steam, and one third was diesel. By the end of the decade, 97 percent of the locomotives were diesel, with the handful of steamers in storage never to be used again.  The war had slowed the transition, but it picked up speed during this decade.  For many of us who love to mix steam and diesel on our railroads, this time period is perfect for us to model. 
    In 1950, steam locomotives could be found in nearly all types of service all over the country.  This was the last great exhibition of steam, and some of the finest steam locomotives that we are all familiar with, were built and run during this time period.  You could find 0-6-0's and 0-8-0's switching many yards and industries, local and branch line freights were often seen with 2-8-0's or 2-8-2's, and local passenger trains were seen with a 4-6-0, 4-6-2, or 4-8-2.  Long distance freights were powered by 2-8-2's, 2-8-4's, 2-10-4's, 4-8-2's, 4-8-4's, or 4-6-6-4's.  Heavy trains such as coal and ore trains were the home for the 2-10-2's, 2-10-4's, 2-8-8-2's, and 2-8-8-4's.  The most common wheel arrangements on short lines, were the good old 2-8-0's.  Baldwin, Alco, and Lima, were the big three locomotive builders for the time period.  Many premier passenger trains still had steam to pull them like the Broadway Limited, 20th Century, and the SP Daylight.  Soon, during these years, the diesel would take over, and these once proud steam locomotives would be found pulling short locals or even high speed freight.  
    Diesel locomotives of this era came in three basic configurations; switcher, cab, or road switcher.  This was the time of highly colorful paint schemes, often one for passenger service, one for freight service, and a third for yard switchers.  Switchers generally rode on two axel trucks and were used in all sorts of yard and industrial switching locations.  They had walkways all around, and a platform on each end for the brakeman to safely ride in full view of the engineer.  These units included the familiar S-4 and the NW-2 among others.  Cab units were often two axel or three axel truck diesels.  In most cases the two axel units were freight, and three axel were passenger, but exceptions to the rule can be found.  These were your "E" and "F" units from EMD, and your PA and FA units from Alco.  They were often found in permanent sets of A-B-B-A units and were the glamour girls of many railroads.  Over time it was found that these units were not that useful for switching service, due to poor rear visibility, and lack of platforms for the brakeman.   The road switcher caught on in a big way.  It could be used for freight or passenger service (if equipped with a steam generator), had excellent visibility, had walkways and end platforms for the brakeman.  It was also easy to service, since the whole body had access doors that could be opened from the outside for maintenance.  These units rode on 2 axel trucks like the Geep (GP7/9 ) and the RS-3, but could also come with three axel trucks for heavy road service, like the SD-7 or 9 and the RSD series.
    With both steam and diesel on the nation's rails, the 1950's were a time of motive power variety. Brightly painted passenger diesels rode past older steam locomotives pulling branch line freights.  Beautifully maintained 4-8-4's passed yards being worked by new diesel switchers, or often had an F-Unit helper added for a steep grade ahead.  Commuters often rode to work behind a 4-6-2, and came home behind an RS-3.  This is one of the many reasons why modelers look to this era, and why many model railroads imitate these times. 
     The manufacturers of our Large Scale trains have provided some nicely detailed locomotives for this time period along with appropriate rolling stock including passenger cars and freight cars.  Aristo has the FA and RS-3 along with it's branch line passenger railcar the RDC-1. They offer an 0-4-0 Switcher, a 4-6-2 Pacific, a 2-8-2 Mikado, and a 2-8-8-2 Mallet. Future releases include a 2-8-0, an SD-9, and an E-8.  USA offers it's F3's, PA's, GP7/9, NW-2, S-4, 4-6-4 Hudson, UP Big Boy, and the GG-1.  LGB has it's 2-8-2 Mikado, GG-1 and its Mogul.  Most of these offerings are 1/29 scale or close to it, so there is no problem building a motive power roster for this time period.  
NW-2 (USA)