A locomotive wheel arrangement under the UIC classification indicating two trucks, each with three axles. The outer two axles on each truck have traction motors, while the middle axle is an idler used solely to distribute the locomotive's weight. This setup was common on early passenger diesels to provide a smoother ride and reduce the axle loading on lighter rail.
Heard on the job
The E-units rode like a dream because of that A1A-A1A truck design spreading the weight out.