A2-8-8-2, in theWhyte notation for describingsteam locomotivewheel arrangements, is anarticulated locomotive with a two-wheelleading truck, two sets of eightdriving wheels, and a two-wheeltrailing truck. The equivalentUIC classification is, refined to Mallet locomotives,(1′D)D1′ 4v. These locomotives usually employ theMallet principles of articulation—with the rear engine rigidly attached to the boiler and the front engine free to rotate—andcompounding. The 2-8-8-2 was a design largely limited to American locomotive builders. The last 2-8-8-2 was retired in 1962 from the N&W's roster, two years past the ending of steam though steam was still used on steel mill lines and other railroads until 1983.
Other equivalent classifications are:
A similar wheel arrangemement exists forGarratt locomotives, but is referred to as2-8-0+0-8-2 since both engine units swivel.
The first 2-8-8-2 was built in 1909 byBaldwin, who sold two to theSouthern Pacific Railroad (classifiedMC-1), and then three each to theUnion Pacific Railroad and UP-ownedOregon Railroad and Navigation Company. Baldwin conceived the type as an expansion of the2-6-6-2 permitting a greatertractive effort.
The next order for the type was from the Southern Pacific; these differed in beingcab forward locomotives, so that the crew could have better visibility and breathing in the SP's long tunnels andsnow sheds. They were very successful, and SP continued to order cab-forward locomotives, building an eventual fleet of 256 of numerous classes; later cab-forwards were4-6-6-2s (originally 2-6-6-2s) and4-8-8-2s.
The 2-8-8-2 proved itself to be a capable hauler on mountain grades, enabling the replacement of several smaller locomotives and hauling longer trains than before. Most of them were not fast; they hauled at drag freight speeds, up to 25 mph (40 km/h). However, theNorfolk and Western Y6 class were designed to run up to 55 mph (89 km/h). The locomotives were adopted by a broad spectrum of mountain railroads, including the Norfolk & Western,Southern,Virginian,Great Northern,Clinchfield,Denver & Rio Grande Western,Reading,Western Maryland,Missouri Pacific,Frisco, and theDuluth, Missabe and Iron Range Railway. On many railroads, the locomotives of the type were the most powerful on the roster. When built, the 2-8-8-2s of theWestern Pacific Railroad were among the most powerful steam locomotives in the world and formed the basis for the later2-8-8-4 "Yellowstone" type engines used by the Duluth, Missabe and Iron Range.
The last compoundMallet locomotives to operate on major railroads in the United States were the 2-8-8-2 Y6b class of theNorfolk and Western Railway. After their final modifications in the 1950s, they were said to be capable of 170,000 lbs tractive effort in simple-expansion mode, although some have questioned this claim (the original design tractive effort was 152,206 lbs SIMPLE and 126,838 lbs COMPOUND). The last were retired in May 1960.
As of 2008, there are two surviving 2-8-8-2 locomotives, both former Norfolk & Western.N&W 2050 is from the railroad's Y3a class;Alco's Richmond works built it in 1923 and it is displayed at theIllinois Railway Museum inUnion, Illinois.N&W 2156, the most powerful extant steam locomotive in the world (in terms of tractive effort), is from the railroad's Y6a class; N&W's ownRoanoke Shops built it in 1942 and it is owned by theNational Museum of Transportation inSt. Louis, Missouri. The 2156 was displayed at theVirginia Museum of Transportation inRoanoke, Virginia from 2015 to 2020, after which it returned to the Museum of Transportation in St. Louis.
