The Pennsylvania Railroad

Pennsylvania Railroad

The Pennsylvania Railroad was an American Class I railroad, founded in 1846. Commonly referred to as the "Pennsy", the PRR was headquartered in Philadelphia, Pennsylvania....

's class AA1 comprised two experimental electric locomotives constructed in 1905 by Westinghouse at the start of the PRR's electrification project.
They were testbeds for larger locomotives to come. Both were of B-B wheel arrangement

Wheel arrangement

In rail transport, a wheel arrangement is a system of classifying the way in which wheels are distributed beneath a locomotive.. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and connections, with the adopted notations varying by country...

 in the Association of American Railroads

Association of American Railroads

The Association of American Railroads is an industry trade group representing primarily the major freight railroads of North America . Amtrak and some regional commuter railroads are also members...

 classification scheme; each had two trucks

Bogie

A bogie is a wheeled wagon or trolley. In mechanics terms, a bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in place, as on a cargo truck, mounted on a swivel, as on a railway carriage/car or locomotive, or sprung as in the suspension of a caterpillar...

, 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.

Both locomotives proved unstable at speed, pounding the track with high lateral forces. A competing experimental unit, "Odd D" #10003

PRR Odd D 10003

Pennsylvania Railroad's Odd D #10003 was an experimental electric locomotive built in 1907 of 4-4-0 wheel arrangement in the Whyte notation, or 2-B in the AAR scheme. On the PRR, class D was assigned to 4-4-0 locomotives...

, of 4-4-0

4-4-0

Under the Whyte notation for the classification of steam locomotives, 4-4-0 represents the wheel arrangement of four leading wheels on two axles , four powered and coupled driving wheels on two axles, and no trailing wheels...

 wheel arrangement in Whyte notation

Whyte notation

The Whyte notation for classifying steam locomotives by wheel arrangement was devised by Frederick Methvan Whyte and came into use in the early twentieth century encouraged by an editorial in American Engineer and Railroad Journal...

 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

PRR DD1

The Pennsylvania Railroad's class DD1 were semi-permanently coupled pairs of third rail direct current electric locomotives built for the railroad's initial New York-area electrification. They operated between Manhattan Transfer and Pennsylvania Station in New York City, and from there to the...

 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

Long Island Rail Road

The Long Island Rail Road or LIRR is a commuter rail system serving the length of Long Island, New York. It is the busiest commuter railroad in North America, serving about 81.5 million passengers each year. Established in 1834 and having operated continuously since then, it is the oldest US...

in 1916. Numbered 323 on that road and nicknamed "Phoebe", the locomotive was in use until 1937 when it was scrapped.
No. 10002, meanwhile, was renumbered #3951 and continued in service on the PRR.