A1A-A1A
"A1A-A1A" means there are two trucks under the unit. Each truck has one powered axle, one idler axle, and one more powered axle. This was to more evenly spread the weight of the locomotive over the track. Examples include the EMD E-units and ALCO PAs, which were passenger locomotives, and the dual service FM Erie-built. BNSF is scheduled to take delivery of ES44C4 locomotives with this type of truck in 2009.
Read more about this topic: AAR Wheel Arrangement