Pennsylvania Railroad Class DD1

The PRR DD1s were semi-permanently coupled pairs of third rail direct current electric locomotives built for the railroad's initial New York-area electrification. 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.

These engines were all built by the PRR's own Altoona Shops in 1911 for the Pennsylvania Railroad. They operated between Manhattan Transfer and Pennsylvania Station in New York City, and thence to the coach yards at Sunnyside Yard in Queens, New York.

Each half-locomotive contained one large electric motor mounted in the body and driving via a jackshaft and side rods.

The locomotives have Resistance controlled DC current supplied to DC motors connected to the axles through Jackshaft and side rods

The DD1s' electric motors gave them 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.

Today, only one pair, Nos. 3936 and 3937, survives. This pair is at the Railroad Museum of Pennsylvania on static display and was listed on the National Register of Historic Places.

Trivia

• The first DD1-class of locomotives were introduced into regular passenger service on November 27, 1910 to operate in the North River Tunnels under the Hudson River.
• Some of the DD1's operated on the PRR-owned Long Island Rail Road's extensive third rail network.
• As the new L5s were being introduced in 1924, most DD1s were transferred to the Long Island Railroad.
• The Long Island Railroad scrapped most of their DD1's from 1949 to 1951, and only two pairs Nos. 3936 and 3937 remained in 1962.
• Each of these locomotives had its own Westinghouse 315-A, direct current, commutating pole, electric motors within a monocoque cab.
• New Electrics like the famous sleek GG1 gradually replaced the older DD1s.
• In the AAR wheel arrangement notation, this is described as 2B+B2.
• 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.
• Each half-locomotive contained one large electric motor mounted in the body and driving via a jackshaft and side rods.
• These engines current supplied to DC motors connected to the axles through Jackshaft and side rods.
• The DD1 locomotives operated off of 650 volt direct current from a third rail.

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