A railroad engineer, locomotive engineer, train operator, train driver, engine driver or loco pilot is a person who operates a train on a railroad or railway. The locomotive / railroad engineer is in charge of and responsible for driving the locomotive(s) as well as the mechanical operation of the train, train speed, and all train handling. The use of the term engineer to describe this occupation should not be confused with professional engineer.
For many United States (US) railroads, the following career progression is typical: assistant conductor (brakeman), conductor and finally engineer. In the US, engineers are required to be certified and re-certified every two to three years.
In India, a loco pilot starts as a diesel assistant or electrical assistant (in case of electric locomotives). They then get promoted on a scale: goods, passenger, Mail/Express and Rajdhani/Shatabdi/Duronto. 
In the United States, Canada, and New Zealand, train drivers are known as "locomotive engineers". In the United Kingdom, South Africa, and Australia, they are known as "train drivers", "engine drivers", "locomotive drivers", or "locomotive operators".
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An engineer is responsible for preparing equipment for service, checking paperwork and the condition of the locomotives. Their duties require that they control acceleration, braking and handling of the train underway. They must know the physical characteristics of the railroad, including passenger stations, the incline and decline of the right-of-way and speed limits. Along with the conductor, the engineer monitors time to not fall behind schedule, nor leave stations early. The train's speed must be reduced when following other trains, approaching route diversions, or regulating time over road to avoid arriving too early. The engineer assumes the duties of the conductor if the conductor is incapacitated.
The locomotive engineer is required to have an intimate knowledge of track geometry including signal placement so as to be able to safely control their train.
Maintaining concentration is of critical importance in this role.
Train dynamics can be extreme and therefore an engineer must be familiar with train handling techniques so as to avoid train partings, derailments and not exceeding line speed.
Freight trains typically have different train forces from passenger trains. A typical freight train may have 500 tonnes of locomotive weight at the front. That may be followed by 1500 m of wagons. The wagons may or may not be uniformly loaded and may brake differently.
Severe brake applications can combine with these factors to cause a train parting. Therefore good train handling practice for freight trains is usually to keep the consist (rail vehicles which make up a train) stretched. This is achieved by keeping the consist in power while a brake application is made and by bleeding the air off the locomotives brakes before they apply. It is not possible to do this with the use of dynamic brake, which presents its own train handling challenges.
When there are multiple locomotives, some may be set up to brake like wagons instead of locomotives, as too many locomotives on the front of the train (all with brakes bled off) would require too heavy an application from the rest.
On shorter passenger trains, this is even more noticeable, requiring the first application of the brake to be bled off on the locomotive, applying locomotive brakes with subsequent increases in application. The length and make-up of the slowing or stopping distance dictates just how much locomotive brake application should be allowed to apply.
The use of dynamic brake can result in a severe slack action, when engaged, run in is highly possible if brought in at an inappropriate time (regarding track geometry and train speed) and if disengaged at an inappropriate time can result in a run out. Both can potentially snap train drawgear or couplings.
Straightlining is a potential cause of derailment that train handling techniques must take into account in order to reduce the likelihood of occurrence. When a train rounds a curve basic physics dictates the trailing wagons in the consist will try to take the shortest route and the flange on some of the wheels within the consist could potentially fail to prevent this occurring with the resultant effect being a derailment.
Track geometry is also critical to train handling. It is desirable to have brakes releasing at the bottom of steep grades rather than applied. And at the top of a steep grade it is desirable to have a fully charged brake pipe.
Serial braking is where a train descends a grade on the air brake alone. The brake pipe application is gradually increased to slow down and if required (depending on the weight of the train and on the grade) stop the train so as to allow the locomotive compressors to recharge the brake pipe throughout the consist. In these cases it is permissible to use the locomotive brakes (which are independent of the train brake and charged through the main reservoir directly) to hold the train (In some cases the weight of the trailing consist will not be held on the locomotive brakes alone) slowing the rate of acceleration and giving more time to recharge the brake pipe to give a better application in the next subsequent train brake application. A runaway can occur if a brake application is required before the train pipe has recharged (as happened at Cima Hill in the United States).
A split reduction is where a train brake application is made and gradually increased as the train descends the grade. It is different from serial braking in that with Serial Braking the application is released, the brake pipe recharged then reapplied.
The dynamic brake when operable slows down the rate of acceleration and allows longer for a train brake pipe to be recharged before being required to be re applied. When a train descends a grade utilizing both the dynamic and air brakes the procedure is known as 'maintaining braking'.
In the case of severe grades (for example the Westmere Bank in New Zealand, which is a 1:33 grade with a 40 km/h (25 mph) speed limit) a trains allowable speed is lower for a train that doesn't have dynamic brake than for one that does.
In freight train marshalling yards the wagon brakes are sometimes bled off so they can be easily loose shunted. However when a shunt locomotive moves large numbers of wagons around with no brakes the locomotive must brake for the entire train. This can result in severe slack action and wheel slip. Damage to goods and rolling stock is possible. Also, with unbraked wagons there is potential for a runaway.
Notable railroad engineers/train drivers
- John Axon (UK)
- Ben Chifley, former Prime Minister of Australia
- Casey Jones (US)
- Benjamin Hafner (US)
- Bernard Holden (UK), President of the first preserved standard gauge railway
- Wallace Oakes (UK)
- Norman Kirk, former Prime Minister of New Zealand
- Roy Welensky, former Prime Minister of Rhodesia and Nyasaland
The United Kingdom (UK)-based transport historian Christian Wolmar stated in October 2013 that the train drivers employed by the Rio Tinto Group to transport iron ore across the Australian outback are most likely the highest-paid members of the occupation in the world at that time.
- Huibregtse, Jon R. American Railroad Labor and the Genesis of the New Deal, 1919-1935 (University Press of Florida; 2010; 172 pages)
- Licht, Walter. Working for the Railroad: the organization of work in the nineteenth century (1983)
- Orr, John W. Set Up Running: The Life of a Pennsylvania Railroad Engineman, 1904-1949 (2001)
- Tuck, Joseph Hugh. "Canadian Railways and the International Brotherhoods: Labour Organizations in the Railway Running Trades in Canada, 1865-1914" Dissertation Abstracts International, 1977, Vol. 37 Issue 10, p6681-6681
- White, John H., Jr. "Oh, To Be a Locomotive Engineer," Railroad History, Dec 2003, Issue 189, pp12-33, and Summer 2004, Issue 190, pp 56-76; Examines the role of the railroad engineer 1890 to 1919, discussing qualifications for becoming an engineer and typical experiences on the job.
- "2003 CFR Title 49, Volume 4; Part 240: Qualification and Certification of Locomotive Engineers". Code of Federal Regulations. United States National Archives and Records Administration. Retrieved 2007-11-14.
- "Train Crew". FAQ: Railway Operations. Indian Railways Fan Club. 2007. Retrieved 2007-11-14.
- Elisabeth Behrmann (3 October 2013). "Rio Replacing Train Drivers Paid Like U.S. Surgeons". Bloomberg. Retrieved 3 October 2013.
- A detailed explanation of what train driving involves, and becoming a train driver in the UK
- Run-A-Locomotive. Link to a site that offers an engineer experience program at a museum in California.