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.

4-6-4-4 wheel arrangement
The PRR Q1 6130 - the only locamotive with this wheel arrangement

Other equivalent classifications are:

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.

References

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