Within each of these sets, there is a truck with two idler axles, and inboard of it are four powered axles. Two of these articulated sets are placed back to back and connected by a hinge. Examples include the Baldwin DR-12-8-1500/2 "Centipede" diesel locomotives and the GE "Little Joe" electric locomotives. "B-D+D-B" means there are two sets of articulated axles under the unit. Within each of these sets, there is a truck with two powered axles, and inboard of it are four powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The W-1 class of electric locomotives built by General Electric for the Great Northern Railway used this arrangement.  "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. "(B+B-B+B)+(B+B-B+B)" means there are 2 units, each with 4 trucks in a B+B-B+B wheel arrangement. Example include the Virginian Railway's EL-2B electric locomotives.