4-6-4-4

In Whyte notation, a '4-6-4-4' is a railroad steam locomotive that has four leading wheels followed by six coupled driving wheels, a second set of four driving wheels and four trailing wheels.
The equivalent UIC classification is '2'CB2''. The sole example of this arrangement was the PRR Q1. This locomotive was essentially a prototype in the development of the PRR Q2, a 4-4-6-4.