In the Whyte notation for the classification of steam locomotive wheel arrangement, a 2-6-6-4 is a locomotive with a two-wheel leading truck, two sets of six driving wheels, and a four-wheel trailing truck. All 2-6-6-4s are articulated locomotives, of the Mallet or related simple articulated type. Other equivalent classifications are: * UIC classification: (1'C)C2' (also known as German classification and Italian classification) * French classification: 130+032 * Turkish classification: 34+35 * Swiss classification: 3/4+3/5 In all, sixty 2-6-6-4s were constructed in North America.