In its search for a main line electric locomotive, the motive department of the PRR appeared to be using steam locomotives as a pattern for development. The L-6 had the same wheel arrangement as the "Mikado" (2-8-2) and was to be assigned to freight, while the P5a had the same wheel arrangement as the "Hudson" (4-6-4) and was built for passenger service. The P5a lacked the power to move the longer passenger trains that were needed to serve the increasing traffic in the northeast corridor and the PRR looked at the "Northern" (4-8-4) that was being used by many railroads to haul passenger trains.
The PRR motive power engineers decided to develop a 2-D-2 (4-8-4 wheel arrangement) electric locomotive. They started with the P5a and added an additional driving axle which was powered by two 625 HP motors giving the new locomotive a total of 5,000 HP as compared to the 3,750 HP of the P5a. The diameter of the driving wheels were reduced from 72" to 62" and the overall length increased by two feet and 10,000 lbs was added to the total weight of the locomotive, all of which was over the drivers. This new design was designated as Class R-1.
At the same time, a new box cab electric locomotive was developed for the New Haven Railroad with a 2-C+C-2 wheel arrangement. This Class EP3a locomotive was borrowed by the PPR for testing. The test results were very impressive and a locomotive with this wheel arrangement was specified by the PRR motive power department and it was designated as Class GG-1.
It was decided that a single example of the Class R-1 and the Class GG-1 would be built and then tested to see which would do better in actual operation. Westinghouse was chosen to build the prototype of the Class R-1 and General Electric received an order to build one Class GG-1 locomotive. The PRR engineers seemed to favor the Class R-1 and when it was rolled out of the Westinghouse East Pittsburgh, PA plant, it was wearing road number 4800, the first in the series set aside for the new main line locomotive. The GG-1, built in GE's Erie, PA plant was assigned road number 4899.
Both locomotives were delivered in August of 1934 and were subjected to an extensive series of tests. They underwent ten weeks of tests at the PRR test track near Claymont, DE and in regular passenger service between New York and Philadelphia. Results of the tests conducted at the test track showed that both locomotives were superior to the P5a, but the GG-1 out-performed the R-1. In regular service, the Class R-1, with its long rigid wheel base, had difficulty negotiating some sharp curves and yard turnouts.
As a result of the testing program, the GG-1 was selected, and on November 17, 1934 the PRR ordered 57 Class GG-1 locomotives to be built. The road numbers of the two prototypes were swapped and the Class R-1 with its new number 4899 was put on the roster and was assigned to passenger sevice. It had its road number changed to 4999 when a GG-1 was delivered with number 4899 in May of 1940.
The single Class R-1 regularly hauled the westbound "Broadway Limited" and would often return east with a heavy mail-express train. The R-1 locomotive had difficulty on sharp curves and occasionally it would derail passing a switch in the Sunnyside Yard. The R-1 went to the scrapper in 1958 with the distinction of being the only PRR locomotive with the 4-8-4 wheel arrangement.
|Wheel Arrangement:||2-D-2 (4-8-4)|
|Length:||64' - 8"|
|Width:||10' - 6"|
|Height:||15' - 0" with pantographs down|
|Weight on Drivers:||230,000 lbs|
|Total Locomotive Weight:||402,000 lbs|
|Line Voltage:||11,000 Volts, 25 cycle (HZ) AC|
|Traction Motors:||8 @ 625 HP, single phase|
|Total HP:||5,000 HP|
|Tractive Effort:||18,750 lbs @ 100 mph|
|Gear Ratio:||27:74 (100 mph)|