PRR DD1 Electric Locomotive
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 coach yards at Sunnyside Yard in Queens, New York. Some also operated on the PRR-owned Long Island Rail Road's extensive third rail network. They had a wheel arrangement of 4-4-0+0-4-4 in the Whyte notation; in other words, two 4-4-0 locomotives coupled back-to-back, hence its class letter, as the Pennsylvania listed all 4-4-0s under Class D. In the AAR wheel arrangement notation, this is described as 2B+B2. Each half-locomotive contained one large electric motor mounted in the body and driving via a jackshaft and side rods. Those electric motors gave the DD1 a potential top speed of 85 mph (137 km/h), though PRR/LIRR timetables never allowed more than 65 mph. The simplicity and reliability of these locomotives allowed it to outlast its potential replacement model, the PRR L5.

One pair, Nos. 3936 and 3937, is in the Railroad Museum of Pennsylvania and was listed on the National Register of Historic Places.

Pennsylvania Railroad electric locomotive, class DD1 No. 3998, ca. 1923.  Library of Congress.

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Pennsylvania Railroad electric locomotive, class DD1 No. 3998, ca. 1923.

PRR DD1 Overview
Type and origin
Power type: Electric
Builder: Altoona Works
Build date: 1911
Total produced: 66 (in 33 married pairs)

AAR wheel arrangement: 2-B+B-2
UIC class: 2′B+B2′
Gauge: 4 ft 8 1⁄2 in (1,435 mm) standard gauge
Leading diameter: 36 in (914 mm)
Driver diameter: 72 in (1,829 mm)
Wheelbase: 7 ft 5 in (2.26 m) between driving axles
Length: 64 ft 11 in (19.79 m)
Width: 9 ft 1 in (2.77 m)
Height: 14 ft 8 in (4.47 m)
Adhesive weight: 199,000 lb (90,260 kilograms; 90.26 tonnes)
Locomotive weight: 313,000 lb (142,000 kilograms; 142.0 tonnes)
Electric system(s): 650 V DC Third rail
Current collection: Contact shoe
Traction motors: 2 × 315-A 2,000 hp (1,500 kW)
Transmission: Resistance controlled DC current supplied to DC motors connected to the axles through Jackshaft and side rods.

Performance figures
Maximum speed: 85 mph (137 km/h)
Power output: 1,580 hp (1,180 kW) continuous
Tractive effort: 55,500 lbf (247 kN)

See also:

Electric Locomotives

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