The Whyte notation is a classification method for steam locomotives, and some internal combustion locomotives and electric locomotives, by wheel arrangement. It was devised by Frederick Methvan Whyte, and came into use in the early twentieth century following a December 1900 editorial in American Engineer and Railroad Journal.
Under the Whyte notation for the classification of steam locomotives, 0-4-0 represents one of the simplest possible types, that with two axles and four coupled wheels, all of which are driven. The wheels on the earliest four-coupled locomotives were connected by a single gear wheel, but from 1825 the wheels were usually connected with coupling rods to form a single driven set.
On a steam locomotive, a driving wheel is a powered wheel which is driven by the locomotive's pistons. On a conventional, non-articulated locomotive, the driving wheels are all coupled together with side rods ; normally one pair is directly driven by the main rod which is connected to the end of the piston rod; power is transmitted to the others through the side rods.
The UIC classification of locomotive axle arrangements, sometimes known as the German classification or German system, describes the wheel arrangement of locomotives, multiple units and trams. It is used in much of the world, notable exceptions being the United Kingdom, which uses a slightly simplified form of UIC, and in North America, where the AAR wheel arrangement system is used to describe diesel and electric locomotives. In North America, the Whyte notation is only used for steam locomotives.
The AAR wheel arrangement system is a method of classifying locomotive wheel arrangements that was developed by the Association of American Railroads. Essentially a simplification of the European UIC classification, it is widely used in North America to describe diesel and electric locomotives. It is not used for steam locomotives,, which use the Whyte notation instead.
Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 2-4-4 is a steam locomotive with two unpowered leading wheels followed by four powered driving wheels and four unpowered trailing wheels. This configuration was only used for tank locomotives; no tender locomotives with this wheel arrangement were made.
On a steam locomotive, a trailing wheel or trailing axle is generally an unpowered wheel or axle (wheelset) located behind the driving wheels. The axle of the trailing wheels is usually located in a trailing truck. On some large locomotives, a booster engine was mounted on the trailing truck to provide extra tractive effort when starting a heavy train and at low speeds on gradients.
Co-Co is the wheel arrangement for diesel and electric locomotives with two six-wheeled bogies with all axles powered, with a separate traction motor per axle. The equivalent UIC classification (Europe) for this arrangement is Co′Co′, or C-C for AAR.
B-B and Bo-Bo are the Association of American Railroads (AAR) and British classifications of wheel arrangement for railway locomotives with four axles in two individual bogies. They are equivalent to the B′B′ and Bo′Bo′ classifications in the UIC system. The arrangement of two, two-axled, bogies is a common wheel arrangement for modern electric and diesel locomotives.
The Pennsylvania Railroad's class P5 comprised 92 mixed-traffic electric locomotives constructed 1931–1935 by the PRR, Westinghouse and General Electric. Although the original intention was that they work mainly passenger trains, the success of the GG1 locomotives meant that the P5 class were mostly used on freight. A single survivor, prototype #4700, is at the National Museum of Transportation in St Louis, Missouri.
The Pennsylvania Railroad's class R1 comprised a single prototype electric locomotive constructed in 1934 by the Baldwin Locomotive Works of Philadelphia, Pennsylvania, US, with the electrical equipment by Westinghouse.
In Whyte notation, a 4-6-6-2 is a steam locomotive with four leading wheels in an unpowered bogie at the front of the locomotive followed by two sets of driving wheels with six wheels each, followed by two unpowered trailing wheels at the rear of the locomotive.
Under the Whyte notation for the classification of steam locomotives, 0-8-4 represents the wheel arrangement of no leading wheels, eight powered and coupled driving wheels on four axles, and four trailing wheels on two axles.
Co-Bo or Co′Bo′ is a wheel arrangement in the UIC classification system for railway locomotives. It features two uncoupled bogies. The "Co" bogie has three driven axles and the "Bo" bogie has two.
For more than a century, the Swiss locomotive, multiple unit, motor coach and railcar classification system, in either its original or updated forms, has been used to name and classify the rolling stock operated on the railways of Switzerland. It started out as a uniform system for the classification and naming of all rolling stock, powered and unpowered, but had been replaced and amended by the UIC classification of goods wagons.
Under the French classification system for locomotive wheel arrangements, the system is slightly different for steam and electric/diesel vehicles.
In Whyte notation, a 2-4-6 is a steam locomotive with two unpowered leading wheels followed by four powered driving wheels and six unpowered trailing wheels. This wheel arrangement was only used for tank locomotives; no 2-4-6 tender locomotives were made.
The leading wheel or leading axle or pilot wheel of a steam locomotive is an unpowered wheel or axle located in front of the driving wheels. The axle or axles of the leading wheels are normally located on a leading truck. Leading wheels are used to help the locomotive negotiate curves and to support the front portion of the boiler.
Under the British and Imperial classification scheme of locomotive axle arrangements 1Co+Co1 is a classification code for a locomotive wheel arrangement of two eight-wheeled bogies with an articulated inter-bogie connection, each with three axles powered by a separate traction motor per axle and with the fourth non-powered axle in an integral leading pony truck to reduce the axle load. The similar 1Co-Co1 classification is in the same axle configuration, but without the inter-bogie connection.
Rigid-framed electric locomotives were some of the first generations of electric locomotive design. When these began the traction motors of these early locomotives, particularly with AC motors, were too large and heavy to be mounted directly to the axles and so were carried on the frame. One of the initial simplest wheel arrangements for a mainline electric locomotive, from around 1900, was the 1′C1′ arrangement, in UIC classification.
