Editing Whyte notation (section)

== Structure of the system ==
=== Basic form ===
The notation in its basic form counts the number of [[leading wheels]], then the number of [[driving wheels]], and finally the number of [[trailing wheels]], numbers being separated by dashes.<ref>{{cite web| url=http://www.trains.com/trn/default.aspx?c=a&id=201| title=Builder's plates: A locomotive's birth certificate| publisher=[[Kalmbach Publishing]]| author=Thompson, Keith| date=2006-05-01| access-date=2008-02-08| url-status=live| archive-url=https://web.archive.org/web/20081122011919/http://www.trains.com/trn/default.aspx?c=a&id=201| archive-date=22 November 2008}}</ref> For example, a locomotive with two leading axles (four wheels) in front, then three driving axles (six wheels) and then one trailing axle (two wheels) is classified as a {{whyte|4-6-2}} locomotive, and is commonly known as a ''Pacific''.

=== Denotion of other locomotives ===
=== Articulated locomotives ===
For [[articulated locomotives]] that have two wheelsets, such as [[Garratt locomotive|Garratt]]s, which are effectively two locomotives joined by a common [[boiler]], each wheelset is denoted separately, with a plus sign (+) between them. Thus a 4-6-2-type Garratt is a {{whyte|4-6-2+2-6-4}}. For Garratt locomotives, the plus sign is used even when there are no intermediate unpowered wheels, e.g. the [[LMS Garratt]] {{whyte|2-6-0+0-6-2}}.  This is because the two engine units are more than just [[power bogie]]s. They are complete engines, carrying fuel and water tanks. The plus sign represents the bridge (carrying the boiler) that links the two engines.

Simpler articulated types, such as [[Mallet locomotive|Mallet]]s, have a jointed frame under a common boiler where there are no unpowered wheels between the sets of powered wheels. Typically, the forward frame is free to swing, whereas the rear frame is rigid with the boiler. Thus, a [[Union Pacific Big Boy]] is a {{whyte|4-8-8-4}}: four leading wheels, one group of eight driving wheels, another group of eight driving wheels, and then four trailing wheels. Sometimes articulated locomotives of this type are denoted with a “+” between each driving wheels set (so in the previous case, the Big Boy would be a 4-8+8-4). This may have been developed to distinguish articulated and duplex arrangements; duplex arrangements would get a “-“ being rigid and articulated locomotives would get a “+” being flexible. However, given all the wheel arrangements for duplex locomotives have been mutually exclusive to them, it is usually considered unnecessary and thus another “-“ is usually used.

[[Triplex locomotive]]s, and any theoretical larger ones, simply expand on basic articulated locomotives, for example, [[2-8-8-8-2]]. In the case of the Belgian [[quadruplex locomotive]], the arrangement is listed as 0-6-2+2-4-2-4-2+2-6-0.<ref>{{cite web | url=http://www.douglas-self.com/MUSEUM/LOCOLOCO/francocrosti/francocrosti.htm#b | title=The Franco-Crosti Boiler System }}</ref>

=== Duplex locomotives ===
For [[duplex locomotive]]s, which have two sets of coupled driving wheels mounted rigidly on the same frame, the same method is used as for [[Mallet (locomotive)|Mallet]] [[#Articulated locomotives|articulated locomotives]] – the number of leading wheels is placed first, followed by the leading set of driving wheels, followed by the trailing set of driving wheels, followed by the trailing wheels, each number being separated by a hyphen.

=== Tank locomotives ===
A number of standard suffixes can be used to extend the Whyte notation for [[tank locomotives]]:<ref name=irs>{{irs-el|el=17}}</ref>

{|class="wikitable"
!Suffix
!Meaning
!Example
|-
|[No Suffix]
|[[Tender locomotive]]
|{{whyte|0-6-0}}
|-
|T
|[[Tank locomotive]]
|{{whyte|0-6-2|T}}
|-
|ST
|[[Saddle tank locomotive]]
|{{whyte|0-4-0|ST}}
|-
|WT
|[[Well tank locomotive]]
|{{whyte|0-4-0|WT}}
|-
|PT
|[[Pannier tank locomotive]]
|{{whyte|0-6-0|PT}}
|-
|C or CT
|[[Crane tank locomotive]]
|{{whyte|0-6-2|CT}}
|-
|IST
|[[Inverted saddle tank locomotive]]
|{{whyte|0-4-2|IST}}
|-
|T+T (or ST+T, WT+T, etc.)
|[[Tank locomotive#Tender-tank|Tender-tank locomotive]]
|{{whyte|0-4-0|T|T}}
|-
|WT
|[[Tank locomotive#Wing tank|Wing tank locomotive]]
|[[0-4-0]][[Tank locomotive#Wing tank|WT]]
|-
|RT
|[[Tank locomotive#Rear tank|Rear tank locomotive]]
|[[0-4-4T|0-4-4]][[Tank locomotive#Rear tank|RT]]
|}

=== Other steam locomotives ===
Various other types of steam locomotive can be also denoted through suffixes:<ref name=irs/>
{|class=wikitable
|colspan=2|VB or VBT
|[[Vertical boilered locomotive]]
|{{whyte|0-6-0|VB}}
|-
|colspan=2|F
|[[Fireless locomotive]]
|{{whyte|0-6-0|F}}
|-
|colspan=2|CA
|[[Compressed air locomotive]]
|{{whyte|0-6-0|CA}}
|-
|colspan=2|R
|[[Railcar]]
|{{whyte|0-4-4-0|R}}
|-
|colspan=2|R or RT
|[[Rack locomotive]]
|{{whyte|0-4-0|RT}}
|}

=== Internal combustion locomotives ===
{{redirect|8w (locomotive)||8W (disambiguation)#Rail transport}}
The wheel arrangement of small [[Diesel locomotive|diesel]] and [[Petrol locomotive|petrol]] locomotives can be classified using the same notation as steam locomotives, e.g. 0-4-0, 0-6-0, 0-8-0. Where the axles are coupled by chains or shafts (rather than side rods) or are individually driven, the terms 4w (4-''wheeled''), 6w (6-wheeled) or 8w (8-wheeled) are generally used. For larger locomotives, the [[UIC classification]] is more commonly used.

Various suffixes are also used to denote the different types of internal combustion locomotives:<ref name=irs/>
{|class=wikitable
!Suffix
!Meaning
!Example
|-
|PM
|[[Petrol-mechanical locomotive]]
|{{whyte|4w|PM}}
|-
|PE
|[[Petrol-electric locomotive]]
|{{whyte|0-6-0|PE}}
|-
|D
|[[Diesel locomotive]]
|{{whyte|6w|D}}
|-
|DM
|[[Diesel–mechanical locomotive]]
|{{whyte|8w|DM}}
|-
|DE
|[[Diesel–electric locomotive]]
|{{whyte|0-4-0|DE}}
|-
|DH
|[[Diesel–hydraulic locomotive]]
|{{whyte|0-6-0|DH}}
|}

=== Electric locomotives ===
The wheel arrangement of small [[electric locomotive]]s can be denoted using this notation, like with [[#Internal combustion locomotives|internal combustion locomotives]].

Suffixes used for electric locomotives include:
{|class=wikitable
!Suffix
!Meaning
!Example
|-
|BE
|[[Battery-electric locomotive]]
|{{whyte|4w|BE}}
|-
|OE
|[[Electric locomotive#Overhead lines|Overhead-lines electric locomotive]]
|{{whyte|0-8-0|OE}}
|-
|RE
|[[Third rail|Third rail electric locomotive]]
|{{whyte|4w|RE}}
|}