Locomotive Types

Steam Locomotives

Wheel Arrangements and Names

Name(s) applied
to this type
Use* PRR
2-2-0 Planet P/F      
2-2-2   P   (inspection loco) single engine known
4-2-0 Jervis ?      
4-2-2 Bicycle P      
0-4-0 Four-coupled S A A  
2-4-2 Columbia P      
0-4-0 American or Eight-wheeler F/P D D  
4-4-2 Atlantic P E P
(rebuilt from
4-4-4 Reading P O-1
(rebuilt to
0-6-0 Six-coupled S B B  
2-6-0 Mogul F/P F    
2-6-2 Prairie F/P J-28    
2-6-4 Adriatic P   Q
(tank engine)
4-6-0 Ten-wheeler F/P G L  
4-6-2 Pacific P K G  
4-6-4 Baltic or Hudson P P
0-8-0 Eight-coupled S C-1 E  
2-8-0 Consolidation F H I  
2-8-2 Mikado or MacArthur F L M  
2-8-4 Berkshire or Kanawha(C&O) F/P      
4-8-0 Twelve-wheeler F/P      
4-8-2 Mountain or Mohawk F/P M-1    
4-8-4 Northern or Niagara or Greenbrier or Pocono or Dixie or Confederation F/P R-1
6-8-6   F S-2
0-10-0 Ten-coupled S      
0-10-2 Union S      
2-10-0 Decapod F I-1    
2-10-2 Santa Fe F N K  
2-10-4 Texas F J-1    
4-10-0 Mastodon or Gobernador F/P      
4-10-2 Southern Pacific(SP) or Overland(UP) F      
4-12-2 Union Pacific F      
0-4+4-0   F/P AA-1
  F L-5
  Rigid Frame
  P T-1   Rigid Frame
4-4+4-4   F/P DD-1
  P S-1   Rigid Frame
2-4+6-2   F     Articulated
  F Q-1   Rigid Frame
  F Q-2   Rigid Frame
0-6+6-0   F     Articulated
2-6+6-0   F     Articulated
2-6+6-2   F/P FF
2-6+6-4   F     Articulated
2-6+6-6 Allegheny or Alleghany or Blue Ridge(VGN) F     Articulated
4-6+6-4 Challenger F/P GG-1
0-8+8-0   F CC-1s   Articulated
2-8+8-0   F HC-1s N-1
2-8+8-2   F HH-1s N-1
(as built)
2-8+8-4 Yellowstone F     Articulated
4-8+8-4 Big Boy F     Articulated
2-10+10-2   F     Articulated
2-8+8+8-2 Triplex F     Articulated
2-8+8+8-4 Triplex F     Articulated
Wheel arrangements are listed using the Whyte system; the first number is the number of guide wheels at the front of the engine, the last number is the number of guide wheels at the back of the engine, the numbers in the middle are the number of driving (powered) wheels. Plus signs show articulation joints, hyphens show separation between sets of wheels otherwise. Most engines with more than one set of driving wheels were articulated, but a few types, such as the 4-4-4-4 (PRR T-1) had rigid frames. PRR also had two classes, the Q-1 and Q-2, which had the same number of drivers, in two different configurations. PRR’s articulated engines had double-letter classes, as in "GG-1" presumably since the wheel arrangement was the same as two "G" class ten-wheelers back-to-back. Most PRR electrics were articulated, with the L-5, L-6 and the R-1 being exceptions to this general rule. Names were given to types of engines by railroads and by railfans. Some wheel arrangements were given different names on different railroads, for example: the New York Central, which advertised a "water-level route" did not want a "Mountain" type locomotive, but they did want a 4-8-2, so they renamed theirs "Mohawks" after a river in New York. As long as they were at it, they renamed several other types after rivers as well, the Hudson being the best-known. Some Southern railroads did not want to call their 4-8-4 locomotives "Northerns" so they called them by several other names. During WWII, some patriotic railroaders objected to the "Mikado" name used for 2-8-2 engines, and renamed them "MacArthurs" at least for the duration of the war.

*Use: F=Freight, P=Passenger, S=Switching. Uses varied depending on conditions, from one railroad to another, and over time. The notes on this list are to give an idea of the usual use for each type on most railroads.

Diesel Locomotives

In the world of railroads, properly identifying various diesel locomotive models (officially known as diesel-electric locomotives) is a bit of an acquired skill that can take a fair amount of time, especially if you are completely "green" and know little about them. Here are some steps to help.

 If you are entirely new to identifying diesel locomotives, pick up a good book (one of the best to get started is Brian Solomon's "American Diesel Locomotive") on the subject to get yourself familiar with the various locomotive manufacturers with the most common names being: the American Locomotive Company (Alco), Baldwin-Lima Locomotive Works(BLW), Fairbanks-Morse (F-M), General Motors' Electro-Motive Division (EMD), and General Electric (GE).

Today, only the latter two companies still produce diesels for the railroading sector although at least a few models built by all of the companies listed above still operate in some capacity. In any event, for purposes of time this article will only highlight the general differing spotting features among different manufacturers and model types. Diesel locomotives have three basic types; switchers (usually found switching cars in yards), road switchers (typically used in everyday freight service they provide more power than switchers), and cab units which usually feature some type of streamlining and a full-length hood with no "porch" or walkway alongside the locomotive.

Among switchers, EMD's models, as are most of their locomotives in general, feature smooth, distinct lines and contours with the cab set to one end of the locomotive with a signature conical stack(s) protruding from the top of the hood. Except for a few models EMD's switchers were short, typically only around 45 or so feet in length. Models included: SW-1, NW-2, SW-7, SW-9, SW-1200, and SW-1500.General Electric's switchers were distinct and very short. While their larger 70-ton model featured an end-cab design, their switchers were commonly center-aligned. They were highly sought for industrial work since their small frame allowed them to negotiate tight curves and clearances often found within plants and other industrial workplaces. Models included a 44-ton and a 45-ton.Alco's switchers, as with most of their models, are defined aesthetically by rounded corners and roof lines. Their "S" and "T" models featured end-cabs and one single stack protruding from the roof with the latter model featuring a notched nose for the number boards. While technically a road-switcher, Alco's very popular RS series was often used by railroads in switching service. Featuring a cab offset to one end and a long hood with its trademark rounded edges and lines, the RS series is still universally recognized today.Baldwin-Lima-Hamilton's S-12 featured an end-cab design with a very long sweeping front hood with an extended front step leading out of the cab. Never very popular, few of these brutes still operate today.F'M's switcher models included the H-10-44 and the H-12-44, featuring an end-cab that rose flush with the top of the long hood, which was rounded off along the edges.3Among road-switchers, in regards to the classic first and second-generation models, EMD and GE's are the most easily recognizable.

EMD's designs, as usual, are typically very clean in look with a angled and pointed short front hoods with a finished angled-off appearance to the rear of the long hood. Perhaps their most distinguishable features is the angled and protruding dynamic brake housing centered on the top of the long hood and a fuel tank that is smooth and streamlined. Models included: GP-7, GP-9, GP-20, GP-30, GP-40, and GP-50.GE's models are vastly different and very boxy in appearance with clean, crisp lines, a short, stubby short front hood and a radiator housing that is often "winged" in appearance protruding from the rear of the long hood (one of GE's most distinguishing features).Alco's models are typically easily identified by their rounded edges and notched features on the front and rear of the locomotive. Models included: RS-2, RS-3, RSD-4/5, RS-11, and RS-15. Their large Century series road-switchers are very bulky and tall in appearance, but can usually be identified from GEs and EMDs by their rounded cab roofs, short, stubby short front hood and protruding front number plates directly above the windshield. These models included: C420, C424, C415, and C628.F-M's most popular road-switcher was the H-24-66, the Train Master. It was very tall, bulky and boxy featuring an offset cab that rose flush with the roof line. Similar, but somewhat smaller locomotives included the H-16-44 and the H-16-66 models.4In terms of cab units, EMD's were easily the most popular with their E (for passenger service) and F (for freight service) series selling by the thousands. These models are easily recognizable by their clean, "bull dog"-like noses and portholes along their flanks. Both models featured very streamlined carbodies making them all ideal for passenger service although the E series was particularly equipped for the purpose.

Alco's cab units may not have been as popular but were striking nonetheless. Their FA (for freight service) and PA (for passenger service) models featured very automobile-like styling with a long, sweeping front nose and rounded windshields. The PA was the most striking and as often been credited as the most beautiful diesel locomotive ever built.FM's “Consolidation Line” was one of its offerings in the cab unit world. The model, built to both freight and passenger specifications featured a short, almost stubby front nose that was somewhat rounded but also pointed. It only sold a few hundred units and was never very popular. Another F-M cab unit was the Erie-built, named as it was built in Erie, PA.5Today's newest diesel models come from only GE and EMD, the latter now its own company known as Electro-Motive Diesel. The newest EMD unit is the SD70ACe with its most recognizable feature being the extended front nose and offset "winged" radiator housing to the rear.

GE's newest model is the ES or Evolution Series and features now-common GE trademarks like the angled, but clean sweeping front nose and radiator housing to the rear of the long hood. It should be noted that all of today's newest locomotives now feature the "safety cab" which gives models a more streamlined look but no longer allowing the crew to step out onto the front of the locomotive walkway directly from the cab (they must exit from a door on the front of the nose).

Updated November 25, 2010