From 1985, steam locomotives were phased out and electric and diesel locomotives, along with a few CNG (compressed natural gas) locomotives are used.
Steam locomotives are used only in heritage trains.
Locomotives in India are classified by gauge, motive power, the work they are suited for, and their power or model number.
Their four- or five-letter class name includes this information.
The first letter denotes the track gauge, the second their motive power (diesel or electric), and the third their suitable traffic (goods, passenger, multi or shunting).
The fourth letter denoted the locomotive's chronological model number, but in 2002, a new classification was adopted in which the fourth letter in newer diesel locomotives indicate horsepower range.

A locomotive may have a fifth letter in its name, denoting a technical variant, subclass, or sub-type (a variation in the basic model (or series) or a different motor or manufacturer).
In the new diesel-locomotive classification, the fifth letter refines the horsepower in 100-hp increments: A for 100 hp, B for 200 hp, C for 300 hp and so on.
In this classification, a WDM-3A is a 3100 hp, a WDM-3D a 3400 hp and a WDM-3F a 3600 hp locomotive.
Diesel locomotives are fitted with auxiliary power units, which saves almost 88 percent of fuel during the idle time when a train is not running.
From 1985, steam locomotives were phased out and electric and diesel locomotives, along with a few CNG (compressed natural gas) locomotives are used. Steam locomotives are used only in heritage trains. Locomotives in India are classified by gauge, motive power, the work they are suited for, and their power or model number. Their four- or five-letter class name includes this information. The first letter denotes the track gauge, the second their motive power (diesel or electric), and the third their suitable traffic (goods, passenger, multi or shunting). The fourth letter denoted the locomotive's chronological model number, but in 2002, a new classification was adopted in which the fourth letter in newer diesel locomotives indicate horsepower range.
A locomotive may have a fifth letter in its name, denoting a technical variant, subclass, or sub-type (a variation in the basic model (or series) or a different motor or manufacturer). In the new diesel-locomotive classification, the fifth letter refines the horsepower in 100-hp increments: A for 100 hp, B for 200 hp, C for 300 hp and so on. In this classification, a WDM-3A is a 3100 hp, a WDM-3D a 3400 hp and a WDM-3F a 3600 hp locomotive. Diesel locomotives are fitted with auxiliary power units, which saves almost 88 percent of fuel during the idle time when a train is not running.
Indian Railways