機車軸式

在鐵路技術上，機車軸式，或稱機車輪式，是指用英文字母和阿拉伯數字的組合來表達鐵路機車走行部車軸排列結構和特點的系統化分類方式。世界上各地使用的機車軸式表達系統主要有三種。

- 華氏輪式：這是最早出現的機車軸式分類系統之一，廣泛應用於蒸汽機車的識別，主要為美國、加拿大、英國、愛爾蘭等地採用。
- AAR軸式：是一種由美國鐵路協會所制定的軸式分類法，主要應用於美國和加拿大的柴油機車和電力機車。
- UIC分類法：是一種由國際鐵路聯盟制定的軸式分類法，廣泛應用於歐洲和亞洲國家。

## 不同機車軸式之對比

UIC軸式VDEV/VMEV/UIC-System｜華氏式別（Whyte-Notation）｜美式稱呼｜簡單圖解左方為機車前進方向

A1｜0-2-2｜Oo

A2｜0-2-4｜Ooo

1A｜2-2-0｜Planet｜oO

1A1｜2-2-2｜Patentee｜oOo

1A2｜2-2-4｜oOoo

2′A｜4-2-0｜Crampton, Norris, Jervis｜ooO

2′A1｜4-2-2｜Single Driver｜ooOo

2A2｜4-2-4｜ooOoo

3A｜6-2-0｜Crampton｜oooO

N/A｜0-3-0｜OOO

B｜0-4-0｜Four-Wheel-Switcher｜OO

B1｜0-4-2｜OOo

B2′｜0-4-4｜Forney｜OOoo

B3′｜0-4-6｜OOooo

1B｜2-4-0｜Hanscom｜oOO

1′B1′｜2-4-2｜Columbia｜oOOo

1B2′｜2-4-4｜oOOoo

1B3′｜2-4-6｜oOOooo

2′B｜4-4-0｜American, Eight-Wheeler｜ooOO

2′B1′｜4-4-2｜Atlantic｜ooOOo

2′B2′｜4-4-4｜Jubilee｜ooOOoo

2′B3′｜4-4-6｜ooOOooo

C｜0-6-0｜Six-Wheel-Switcher｜OOO

C1｜0-6-2｜OOOo

C2′｜0-6-4｜OOOoo

1′C｜2-6-0｜Mogul｜oOOO

1′C1′｜2-6-2｜Prairie｜oOOOo

1′C2′｜2-6-4｜Adriatic｜oOOOoo

1′C3′｜2-6-6｜oOOOooo

2′C｜4-6-0｜Ten-Wheeler｜ooOOO

2′C1′｜4-6-2｜Pacific｜ooOOOo

2′C2′｜4-6-4｜Hudson, Baltic｜ooOOOoo

D｜0-8-0｜Eight-Wheel-Switcher｜OOOO

D1｜0-8-2｜OOOOo

D2′｜0-8-4｜OOOOoo

D3′｜0-8-6｜OOOOooo

1′D｜2-8-0｜Consolidation｜oOOOO

1′D1′｜2-8-2｜Mikado｜oOOOOo

1′D1′｜2-8-2T｜MacArthur｜oOOOOo

(1′D1′)(1′D1′)｜2-8-2+2-8-2｜Double Mikado, Garrett｜oOOOOo+oOOOOo

1′D2′｜2-8-4｜Berkshire｜oOOOOoo

1′D3′｜2-8-6｜oOOOOooo

2′D｜4-8-0｜Twelve-Wheeler, Mastodon｜ooOOOO

2′D1′｜4-8-2｜Mountain, Mohawk (NYC)｜ooOOOOo

2′D2′｜4-8-4｜Northern, General Service (SP), Golden State (SP), Niagara (NYC), Wyoming｜ooOOOOoo

2D3｜4-8-6｜ooOOOOooo

3′D3′｜6-8-6｜nameless (Pennsylvania Railroad Steam Turbine)｜oooOOOOooo

E｜0-10-0｜Ten-Wheel Switcher｜OOOOO

E1′｜0-10-2｜Union｜OOOOOo

1′E｜2-10-0｜Decapod｜oOOOOO

2′E｜4-10-0｜Mastodon｜ooOOOOO

1′E1′｜2-10-2｜Santa Fe｜oOOOOOo

1′E2′｜2-10-4｜Texas｜oOOOOOoo

2′E1′｜4-10-2｜Southern Pacific, Overland｜ooOOOOOo

F｜0-12-0｜Pennsylvania, Twelve-Wheel-Switcher｜OOOOOO

1′F｜2-12-0｜Centipede｜oOOOOOO

1′F1′｜2-12-2｜Javanic｜oOOOOOOo

2′F1′｜4-12-2｜Union Pacific｜ooOOOOOOo

2′G2′｜4-14-4｜ooOOOOOOOoo

nameless (AA)｜0-2-2-0｜O O

B′B｜0-4-4-0｜nameless (Mallet)｜OO OO

B′B1｜0-4-4-2｜nameless (Mallet)｜OO OOo

2′BB2′｜4-4-4-4｜nameless (Pennsylvania Railroad Duplex)｜ooOO OOoo

3′BB3′｜6-4-4-6｜oooOO OOooo

2′CB2′｜4-6-4-4｜nameless (Pennsylvania Railroad Duplex)｜ooOOO OOoo

C′C｜0-6-6-0｜Erie (Mallet)｜OOO OOO

(1′C)C｜2-6-6-0｜nameless (Mallet)｜oOOO OOO

(1′C)C1′｜2-6-6-2｜Mallet Mogul (SP), Prairie Mallet (ATSF)｜oOOO OOOo

(1′C)C2′｜2-6-6-4｜nameless (Simple articulated)｜oOOO OOOoo

(2′C)C2′｜4-6-6-4｜Challenger (Simple articulated)｜ooOOO OOOoo

(1′C)C3′｜2-6-6-6｜Allegheny (Mallet/Simple articulated)｜oOOO OOOooo

D′D｜0-8-8-0｜Angus (Mallet)｜OOOO OOOO

(1′D)D｜2-8-8-0｜Bullmoose (Mallet)｜oOOOO OOOO

(1′D)D1′｜2-8-8-2｜Chesapeake, Mallet consolidation (Mallet)｜oOOOO OOOOo

(1′D)D2′｜2-8-8-4｜Yellowstone (Mallet/Simple articulated)｜oOOOO OOOOoo

(2′D)D1′｜4-8-8-2｜Cab Forward (Simple articulated)｜ooOOOO OOOOo

(2′D)D2′｜4-8-8-4｜Big Boy (Simple articulated)｜ooOOOO OOOOoo

(1′E)E1′｜2-10-10-2｜Virginian (Mallet)｜oOOOOO+OOOOOo

(2′C1′)(1′C2′)｜4-6-2+2-6-4｜Double Pacific (Garratt)｜ooOOOo+oOOOoo

(2′C2′)(2′C2′)｜4-6-4+4-6-4｜Double Hudson (Garratt)｜ooOOOoo+ooOOOoo

(2′D)(D2′)｜4-8-0+0-8-4｜Double Mastodon (Garratt)｜ooOOOO+OOOOoo

(2′D1′)(1′D2′)｜4-8-2+2-8-4｜Double Mountain (Garratt)｜ooOOOOo+oOOOOoo

(2′D2′)(2′D2′)｜4-8-4+4-8-4｜Double Northern (Garratt)｜ooOOOOoo+ooOOOOoo