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 DD1 were semi-permanently coupled pairs of third rail

Third rail

A third rail is a method of providing electric power to a railway train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track. It is used typically in a mass transit or rapid transit system, which has alignments in its own corridors, fully or almost...

 direct current

Direct current

Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 electric locomotive

Electric locomotive

An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or an on-board energy storage device...

s built for the railroad's initial New York

New York

New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

-area electrification

Electrification

Electrification originally referred to the build out of the electrical generating and distribution systems which occurred in the United States, England and other countries from the mid 1880's until around 1940 and is in progress in developing countries. This also included the change over from line...

. They operated between Manhattan Transfer

Manhattan Transfer (PRR station)

Manhattan Transfer was a passenger station in Harrison, New Jersey, east of Newark, 8.8 miles west of New York Penn Station on the Pennsylvania Railroad main line, now Amtrak's Northeast Corridor...

 and Pennsylvania Station

Pennsylvania Station (New York City)

Pennsylvania Station—commonly known as Penn Station—is the major intercity train station and a major commuter rail hub in New York City. It is one of the busiest rail stations in the world, and a hub for inbound and outbound railroad traffic in New York City. The New York City Subway system also...

 in New York City, and from there to the coach yards at Sunnyside Yard

Sunnyside Yard

Sunnyside Yard is a large coach yard, a railroad yard for passenger cars, in Sunnyside, Queens in New York City.-Description:The yard is owned by Amtrak and is also used by New Jersey Transit. The shared tracks of the Long Island Rail Road Main Line and Amtrak's Northeast Corridor pass along the...

 in Queens, New York. Some also operated on the PRR-owned 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...

's extensive third rail network. They had a wheel arrangement of 4-4-0+0-4-4 in the 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...

; in other words, two 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...

 locomotives coupled back-to-back. In the AAR wheel arrangement

AAR wheel arrangement

The AAR wheel arrangement system is a method of classifying locomotive wheel arrangements that was developed by the Association of American Railroads. It is essentially a simplification of the European UIC classification, and it is widely used in North America to describe diesel and electric...

 notation, this is described as 2B+B2. Each half-locomotive contained one large electric motor

Electric motor

An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

 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. The simplicity and reliability of these locomotives allowed it to outlast its potential replacement model, the PRR L5

PRR L5

The Pennsylvania Railroad's class L5 were the railroad's second generation of production electric locomotives after the DD1, and the last to use a jackshaft and side rods to drive the wheels. The L5 was a single-unit locomotive instead of the twin-unit DD1. Thirteen were built...

.

One pair, Nos. 3936 and 3937

PRR 3936 and 3937

PRR 3936 and 3937, formerly 4781 and 4780 respectively, are a pair of DD1-class electric locomotives located in the Railroad Museum of Pennsylvania in Strasburg, Pennsylvania. The two locomotives are semi-permanently coupled together and were assigned an EZN of 36...

, is located in the Railroad Museum of Pennsylvania

Railroad Museum of Pennsylvania

The Railroad Museum of Pennsylvania is a railroad museum in Strasburg, Lancaster County, Pennsylvania.The museum is located on the east side of Strasburg along Pennsylvania Route 741...

 and was listed on the National Register of Historic Places

National Register of Historic Places

The National Register of Historic Places is the United States government's official list of districts, sites, buildings, structures, and objects deemed worthy of preservation...

.