High Quality Content by WIKIPEDIA articles! Under the Whyte notation for the classification of steam locomotives, 4-6-4 represents the wheel arrangement of four leading wheels on two axles, usually in a leading truck, six powered and coupled driving wheels on three axles, and four trailing wheels on two axles, usually in a trailing truck. In France, where the type was first used, it is known as the Baltic, while it became known as the Hudson in most of North America.