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PRR AA1 10002.jpg
PRR AA1 #10002
Type and origin
Power type Electric
Builder Pennsylvania Railroad Altoona Works,[1] also Westinghouse[2]
Serial number EZN-7, EZN-8[3]
Build date 1905
Total produced 2[1]
AAR wheel arr. B-B[2]
Wheel diameter 56 in (1,400 mm)[2]
Wheelbase Truck: 8.5 ft (2.6 m)
Overall: 26 ft (7.9 m)[2]
Locomotive weight 10001: 87 short tons (79 t)
10002: 97 short tons (88 t)[2]
Electric system(s) 600 V DC[2]
Current collection
Third rail
PRR AA1 #10001[2]

The Pennsylvania Railroad's class AA1 comprised two experimental electric locomotives constructed in 1905 by Westinghouse at the start of the PRR's electrification project.[1][2] They were testbeds for larger locomotives to come. Both were of B-B wheel arrangement in the Association of American Railroads classification scheme; each had two trucks, each with two axles and four wheels.

The first, #10001, used gearless motors attached to the axles. The second, #10002, was built with motors mounted in the truck frames and geared to the wheels. Later on it was given one gearless truck.[2]

Both locomotives proved unstable at speed, pounding the track with high lateral forces. A competing experimental unit, "Odd D" #10003, of 4-4-0 wheel arrangement in Whyte notation or 2-B in the AAR scheme, proved much more stable. It was selected as the basis for the production model, which became the PRR DD1 twin-unit locomotive.

At low speeds in switching service, however, the locomotives were acceptable. The first, #10001, was renumbered #3950 and was sold to the (PRR subsidiary) Long Island Rail Road in 1916. Numbered 323 on that road and nicknamed "Phoebe", the locomotive was in use until 1937 when it was scrapped.[4] No. 10002, meanwhile, was renumbered #3951 and continued in service on the PRR.[5]


  1. ^ a b c Staufer, Alvin F. (1962). Pennsy Power. Staufer. p. 247. LOC 62-20878. 
  2. ^ a b c d e f g h i Burch, Edward Parris (1911). Electric Traction for Railway Trains. New York: McGraw-Hill. 
  3. ^ Britton, Jerry. "Electric Class Cross Reference". Keystone Crossings. Retrieved 2008-05-03. 
  4. ^ Keller, David; Steven Lynch (2005). Revisiting the Long Island Rail Road. Arcadia. p. 12. ISBN 0-7385-3829-9. 
  5. ^ Staufer, Alvin F. (1968). Pennsy Power II. Staufer. p. 124. LOC 62-20872. 

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