A hood unit, in railroad terminology, is a body style for diesel and electric locomotive

Locomotive

A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...

s. On a hood unit, the body of the locomotive is less than full-width for most of the locomotive's length, with walkways on the outside of the locomotive. In contrast, a cab unit

Cab unit

A cab unit and a carbody unit are body styles of locomotives in railroad terminology. While closely related, they are not exactly the same....

 has a full-width carbody for the length of the locomotive. A hood unit has sufficient visibility to be operated in both directions from a single cab

Cab (locomotive)

The cab, crew compartment or driver's compartment of a locomotive is the part of the locomotive housing the train driver or engineer, the fireman or driver's assistant , and the controls necessary for the locomotive's operation....

. Also, the underframe is the main load-bearing member, allowing the hood to be non-structural and easily opened or even removed for maintenance.

History

The hood unit evolved from the switcher

Switcher

A switcher or shunter is a small railroad locomotive intended not for moving trains over long distances but rather for assembling trains ready for a road locomotive to take over, disassembling a train that has been...

 locomotive. A switcher's long hood is normally low enough that the crew can see over it, and there typically is no short hood. Alco introduced the road-switcher concept with the RS-1

ALCO RS-1

The ALCO RS-1 was a 4-axle diesel-electric locomotive built by Alco-GE between 1941 and 1953 and the American Locomotive Company from 1953 to 1960. This model has the distinction of having the longest production run of any diesel locomotive for the North American market.The carbody configuration of...

, which was an enlarged switcher with a short hood ahead of the cab. This was added to provide protection for the crew in case of a collision. The low long hood was retained, though its increased length made visibility over it useless. Later, EMD introduced the GP7

EMD GP7

The EMD GP7 is a four-axle diesel-electric locomotive built by General Motors Electro-Motive Division and General Motors Diesel between October, 1949 and May, 1954. Power was provided by an EMD 567B 16-cylinder engine which generated . The GP7 was offered both with and without control cabs, and...

, which had a similar layout, though both hoods were as high as the cab roof. The high long hood became standard for virtually all hood unit locomotives thereafter.

The long hood of a locomotive is usually about as tall as the cab roof in order to fit the large prime mover

Prime mover (locomotive)

In engineering, a prime mover is an engine that converts fuel to useful work. In locomotives, the prime mover is thus the source of power for its propulsion. The term is generally used when discussing any locomotive powered by an internal combustion engine...

 and the exhaust equipment. Originally the short hood of the locomotive was the same height, which is referred to as a high-nose or, confusingly, high short hood. This was originally done to avoid union conflicts, as the high nose ensured that two crewmen (one on each side of the cab) were required in order to see both sides of the track. After this issue was resolved, the height of the short hood was reduced to increase visibility, creating a low-nose or low short hood locomotive. Some locomotives that were originally built with a high nose were later modified to have a low nose. Lately it has become common to make the short hood not only lower but also full-width, creating a wider nose which is sometimes referred to as a safety cab.

The visibility and access advantages mean that the hood unit is overwhelmingly the most popular style of locomotive in North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

, as well as many other nations.

Operation

Although the crew cabin is centered on some hood units, in most cases the cab is closer to one end of the locomotive than the other, breaking the locomotive up into long hood

Long hood

The long hood of a hood unit-style diesel locomotive is, as the name implies, the longer of the two hoods on a locomotive.-Equipment:...

and short hood

Short hood

The short hood of a hood unit-style diesel locomotive is, as the name implies, the shorter of the two hoods on a locomotive...

sections. It is generally preferred to run a hood unit short hood forward so that the cab is closer to the front, but there is enough visibility in the other direction that they can run long hood forward at regular speeds. Some railroad companies (notably, the Norfolk & Western and the Southern

Southern Railway (US)

The Southern Railway is a former United States railroad. It was the product of nearly 150 predecessor lines that were combined, reorganized and recombined beginning in the 1830s, formally becoming the Southern Railway in 1894...

) ordered locomotives with cabs facing long hood forward so that the short hood is actually the rear of the locomotives, but that practice has become increasingly rare. This was usually done to offer greater protection to the crew in the event of a collision. Other locomotives were set up with dual control stands so that they could operate in both directions, making it unnecessary to turn the locomotive around at the end of a run. Some cabless

B unit

A "B" unit, in railroad terminology, is a locomotive unit which does not have a driving cab, or crew compartment, and must therefore be controlled from another, coupled locomotive with a driving cab . The term booster unit is also used. The concept was largely confined to North America...

 hood units were also built. The long hood ran the whole length of those locomotives. In North America, all locomotives are required to have the letter F printed on the side sill at the end which is normally operated as its front.

Freight-oriented hood units

• GE U30C
  GE U30C
  The GE U30C was one of the earliest successes from General Electric in the diesel locomotive market. With 600 units sold, the U30C proved to be a choice for customers who weren't able to purchase SD40's or SD40-2's from EMD due to mass orders...
  
  
• GE U36B
  GE U36B
  GE U36B was a diesel locomotive produced by General Electric beginning in 1969. The U36B was GE's 3600 horsepower answer to the power race with EMD. Only 3 railroads bought this locomotive.-History:...
  
  
• EMD GP30
  EMD GP30
  The EMD GP30 was a 2,250 hp four-axle B-B diesel locomotive built by General Motors Electro-Motive Division of La Grange, Illinois between July, 1961 and November, 1963...
  
  
• EMD SD60
  EMD SD60
  The EMD SD60 is a 3,800 horsepower 6-axle diesel-electric locomotive built by General Motors Electro-Motive Division. Intended for heavy-duty drag freight or medium-speed freight service, it was introduced in 1984, and production of SD60 variants ran until 1995.- History and development...
  
  
• EMD SD70 series
  EMD SD70 series
  The EMD SD70 is a series of diesel-electric locomotives produced by the Electro-Motive Division of General Motors beginning in 1992. Over 4000 locomotives in this series have been produced, mostly of the SD70M and SD70MAC models. All locomotives of this series are hood units with C-C trucks...
  
  

Great Britain

The term "hood unit" is not used in Britain but a few locomotives of the hood unit type survive, e.g. British Rail Class 09

British Rail Class 09

The British Rail Class 09 is a class of 0-6-0 diesel locomotive designed primarily for shunting and also short distance freight trips along branch lines....

 and British Rail Class 20

British Rail Class 20

The British Rail Class 20, otherwise known as an English Electric Type 1, is a class of diesel-electric locomotive. In total, 228 locomotives in the class were built by English Electric between 1957 and 1968, the large number being in part because of the failure of other early designs in the same...

. Withdrawn hood unit types include:

• British Rail 10800
  British Rail 10800
  British Railways 10800 was a diesel locomotive built by the North British Locomotive Company for British Railways in 1950. It had been ordered by the London, Midland and Scottish Railway in 1946 but did not appear until after the 1948 nationalisation of the railways.Design was by George Ivatt and...
  
  
• British Rail Class 15
  British Rail Class 15
  The British Rail Class 15 diesel locomotives, also known as the BTH Type 1, were designed by British Thomson-Houston, and built by the Yorkshire Engine Company and the Clayton Equipment Company, between 1957 and 1961.- Design history :...
  
  
• British Rail Class 16
  British Rail Class 16
  The North British Type 1 was a type of diesel locomotive ordered under British Railways' 1955 Modernisation Plan. Like other Type 1 designs, they were relatively small locomotives intended primarily for local freight traffic....