Front of locomotive to the left
The single S2, No.
6200, in a PRR promotional image.
Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 6-8-6 represents the arrangement of six (6) unpowered leading wheels arranged into a three-axle leading truck, eight (8) powered driving wheels, and six (6) unpowered trailing wheels arranged into a three-axle trailing truck.
Other equivalent classifications are:
The only known example of the 6-8-6 wheel arrangement is the experimental Pennsylvania Railroad S2 steam turbine locomotive.