4-4-4-4

4-4-4-4

Front of locomotive at left

The Baltimore and Ohio Railroad's #5600 George H. Emerson.

Equivalent classifications UIC class 2'BB2' French class 2222 Turkish class 2424 Swiss class 4/8 Russian class 2-2-2-2

First known tender engine version First use May 1937 Country United States Locomotive B&O Class N-1 Railway Baltimore and Ohio Railroad Designer Baltimore and Ohio Railroad Builder Mount Clare Shops Benefits Decreased wheelbase Drawbacks Premature cylinder wear, cylinder clogging and restricted firebox size

First known "True type" version First use April 1942 Country United States Locomotive PRR class T1 Railway Pennsylvania Railroad Designer Ralph P. Johnson Raymond Loewy Builder Baldwin Locomotive Works Altoona Works Evolved from 4-8-4 Benefits Better high speed performance Drawbacks Wheel slip

A 4-4-4-4 steam locomotive, in the Whyte notation for describing locomotive wheel arrangements, has a four-wheel leading truck, two sets of four driving wheels, and a four-wheel trailing truck. While it would be possible to make an articulated locomotive of this arrangement, the only 4-4-4-4s ever built were duplex locomotives—with two sets of cylinders driving two sets of driven wheels in one rigid frame, essentially a 4-8-4 with divided drive.