Car Company exclusively for the Southern Railway in 1939. 2-B "2-B" means there are two trucks or wheel assemblies. The "2" truck is under the front of the unit, and has two idler axles in a row. The "B" truck is under the rear of the unit, and has two powered axles. Examples include the three lightweight power cars built by ALCO/ACF in 1935 and 1937 for use with the Rebel streamliners. 3-A1A "3-A1A" means there are two trucks or wheel assemblies. The "3" truck is under the front of the unit, and has three idler axles in a row. The "A1A" truck is under the rear of the unit, and has one powered axle, one idler axle, and one more powered axle. An example is the later built FM OP800 railcar, six of which were built by the St. Louis Car Company exclusively for the Southern Railway in 1939. A1-1A "A1-1A" means there are two trucks or wheel assemblies under the unit. Each truck has one powered axle and one idler axle, with the powered axles to the outside. A1A-2 "A1A-2" means there are two trucks. The "A1A" truck is under the front of the unit, and has one powered axle, one idler axle, and one more powered axle. The "2" truck is under the back of the unit, and has two idler axles in a row. An example is the Silver Charger power car for the General Pershing Zephyr. A1A-3 "A1A-3" means there are two trucks. The "A1A" truck is under the front of the unit, and has one powered axle, one idler axle, and one more powered axle. The "3" truck is under the back of the unit, and has three idler axles in a row. An example is the Baldwin DR-6-2-10 cab unit, only one of which was built for the Chicago and North Western Railway in 1948. A1A-A1A "A1A-A1A" means there are two trucks under the locomotive. Each truck has two powered axles, with an idler axle between them. This spreads the weight of the locomotive more evenly over the track and counteracts the tendency of trucks to oscillate at high speeds, which is a problem with two axle trucks. The idler wheels may be smaller than the powered wheels. Examples of locomotives with this wheel arrangement include the EMD E-units and ALCO PAs, which were high speed passenger locomotives, and the dual service FM