4-4-6-2

Under the Whyte notation for the classification of steam locomotive wheel arrangements, a 4-4-6-2 is a locomotive with two pairs of leading wheels, one set of four driving wheels, a second set of six driving wheels, and a pair of trailing wheels.

Other equivalent classifications are:

UIC classification: 2BC1 (also known as German classification and Swiss classification)

Italian and French classification: 220+031

The equivalent UIC classification is refined to (2′B)C1′ for Mallet locomotives.

This wheel arrangement was rare. Two are known to have been built, both as compound Mallet locomotives by Baldwin Locomotive Works in 1909 for the Atchison, Topeka and Santa Fe Railway. They were initially numbered 1300 and 1301 but soon re-numbered 1398 and 1399.

These locomotives were perhaps the first and only attempt in North America to adapt the Mallet-compound design for passenger service, and when delivered were the world's largest passenger locos. With a weight of 376,450 pounds and riding on 73-inch driving wheels, they exerted 53,000 pounds of tractive force. Designed to operate at 36 miles per hour, they achieved 60 mph in tests. But the experiment was unsuccessful: Adhesion stability was a problem, as the front engine tended to slip uncontrollably because of an imbalance of tractive effort at passenger-train speeds (this was a common problem with compound Mallets, at any speed much above walking pace). Both locomotives were rebuilt to non-compound 4-6-2 types in 1915, retained their assigned numbers, were still in use as of 1944, and retired by 1950.

A somewhat more successful passenger Mallet design was a Russian 2-4-4-0 built between 1903 and 1909; the last examples were used into the 1950s.