movers, making each unit essentially a pair of high-powered B-B locomotives on a common frame as far as traction and power was concerned). In fact, a usual consist of a D-D unit included a leading C-C unit and a trailing C-C unit, for a total of about 12,600 HP (with four total prime-movers). With today's higher horsepower C-C units (about 4,300 HP apiece), three such C-C units exceeds the total power of the usual D-D consist by 300 HP (with one fewer prime-mover than a usual D-D consist, thereby significantly improving reliability and dramatically reducing maintenance). Although at this time the term D-D is associated with twin-prime-mover locomotives of high power, this does not preclude the possibility of a D-D with a single prime mover of high power some time in the future, nor of the term being used to describe a two-truck, eight-axle electric locomotive. The EMD DDM45 is a narrow-gauge adaptation of the SD45, which required additional axles due to the use of smaller traction motors. 2-D+D-2 "2-D+D-2" means there are two sets of articulated axles under the unit. 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 "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 "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) "(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. An example was the Virginian Railway's EL-2B electric locomotives. See also Locomotives by wheel arrangement Swiss locomotive and railcar classification UIC classification Wheel arrangement Whyte