1B+D+D+B1
"1B+D+D+B1" means there are four sets of articulated axles under the unit. At each end there is one unpowered axle and two powered axles, hinged to a set of four powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The "Bi-Polar" electric locomotives used by the Milwaukee Road used this arrangement.
Read more about this topic: AAR Wheel Arrangement