USRA standard

TheLight Mikadowas the standard light freight locomotive and the most widely built type of the USRA standard designs.

TheUSRA standardlocomotivesandrailroad carswere designed by theUnited States Railroad Administration,thenationalizedrail system of theUnited StatesduringWorld War I.1,870steam locomotivesand over 100,000 railroad cars were built to these designs during the USRA's tenure. The locomotive designs in particular were the nearest the Americanrailroadsandlocomotive buildersever got to standard locomotive types, and after the USRA was dissolved in 1920 many of the designs were duplicated in number, 3,251 copies being constructed overall. The last steam locomotive built for aClass I railroadin the United States, an0-8-0built by theNorfolk and Western Railwayin 1953, was a USRA design. A total of 97 railroads used USRA or USRA-derived locomotives.

Steam locomotive types

The USRA developed designs for0-6-0and0-8-0switcher locomotives,2-6-6-2and2-8-8-2Mallet locomotives,and both light and heavy versions of the2-8-2,2-10-2,4-6-2,and4-8-2types. The light versions were designed with anaxle loadof 54,000 lb (24,500 kg) permitting usage on the vast majority of railroads, while the heavy versions were designed to a maximum axle load of 60,000 lb (27,200 kg) for lines with more heavily constructed track.

The U.S.R.A. also distributed2-10-0 Decapods of Russian designto railroads under its control.

USRA 0-6-0

255 of theUSRA 0-6-0design were built, as well as a great many copies.

USRA 0-8-0

175 of theUSRA 0-8-0design were built, and it was copied extensively thereafter.

USRA Light 2-8-2 "Mikado"

614 of theUSRA Light Mikadotype were constructed, making it the most populous USRA type.

USRA Heavy 2-8-2 "Mikado"

233 of theUSRA Heavy Mikadoswere built.

USRA Light 2-10-2 "Santa Fe"

94USRA Light Santa Felocomotives were constructed.

USRA Heavy 2-10-2 "Santa Fe"

175USRA Heavy Santa Felocomotives were built.

USRA Light 4-6-2 "Pacific"

106USRA Light Pacificswere constructed.

USRA Heavy 4-6-2 "Pacific"

20USRA Heavy Pacificswere built.

USRA Light 4-8-2 "Mountain"

47 of theUSRA Light Mountaintype were built.

USRA Heavy 4-8-2 "Mountain"

15USRA Heavy Mountainswere constructed.

2-6-6-2

30 of theUSRA 2-6-6-2type were built.

2-8-8-2

106 of theUSRA 2-8-8-2locomotives were constructed. TheNorfolk and Western Railway,in particular, continued building this type after the USRA period, developing and modernising it over time, as its Class Y. A N&W Y6B was the last conventional freight-hauling steam locomotive built in the United States.

Freight cars

As part of the USRA, two commonboxcardesigns were developed: a single sheathed car and a double sheathed car. When the USRA boxcars were being designed there wasn't an industry consensus on which was better, so both were built. Freight car design was still in flux in the early part of the 20th century. As John White points out inThe American Freight Car,most cars were really composites, not completelywoodorsteel,and even after steel cars had become the norm, wood had its uses and advantages. Still, steelunderframeshad come to replace wood underframes, but asmetallurgyimproved, there were new designs developed that took advantage of the improved technology. USRA double sheathed boxcars had a fishbelly underframe while the USRA single sheathed cars did not. In general, double sheathed boxcars are likegirder bridges,so all the support needs to come from the frame. Those cars need a stronger frame, hence the fishbelly underframe. Single sheathed cars are liketruss bridges,with the metal side bracing acting as the main structural support for the "bridge." While some engineers did not trust the steel bracing to support a single sheathed car and ordered fishbelly frames for strength, others valued the savings in weight and ordered cars with simpler frames like the USRA SS design.

Type of cars built by the USRA

Type	USRA Specification	Number of cars produced
50-ton Single-Sheathed Box Car	1001-B	25,000
50-ton Drop-BottomGondola	1002-B	20,000
40-ton Double-Sheathed Box Car	1003-B	25,000
55-ton Steel TwinHopper	1005-B	5,000
70-ton Steel Drop-End Mill Gondola	1006-B	5,000