Editing Train (section)

== Motive power ==
{{Main|Locomotive}}[[File:0444_BulawayoZimbabwe_19920730.jpg|thumb|[[Garratt locomotive]]s in [[Zimbabwe]]]]

=== Before steam ===
The first trains were rope-hauled, gravity powered or pulled by horses.{{sfn|Herring|2000|p=8}}

=== Steam ===
Steam locomotives work by burning coal, wood or oil fuel in a boiler to heat water into steam, which powers the locomotive's pistons which are in turn connected to the wheels.<ref>{{Cite web|last=McGonigal|first=Robert S.|date=May 1, 2006|title=How a steam locomotive works|url=https://www.trains.com/trn/train-basics/abcs-of-railroading/how-a-steam-locomotive-works/|access-date=2021-11-05|website=Trains|language=en-US}}</ref> In the mid 20th century, most steam locomotives were replaced by diesel or electric locomotives, which were cheaper, cleaner, and more reliable.<ref name="anymore">{{Cite web|last=Nilsson|first=Jeff|date=2013-05-11|title=Why You Don't See Steam Locomotives Anymore|url=https://www.saturdayeveningpost.com/2013/05/locomotive-diesel-engine/|access-date=2021-11-05|website=The Saturday Evening Post|language=en-US}}</ref> Steam locomotives are still used in [[heritage railway]]s operated in many countries for the leisure and enthusiast market.<ref>{{Cite web|title=Minor and Heritage Railways|url=http://orr.gov.uk/about-orr/who-we-work-with/railway-networks/minor-and-heritage-railways|url-status=live|archive-url=https://web.archive.org/web/20180222044131/http://orr.gov.uk/about-orr/who-we-work-with/railway-networks/minor-and-heritage-railways|archive-date=February 22, 2018|access-date=November 4, 2021|website=orr.gov.uk|publisher=Office of Rail and Road}}</ref>{{globalize-inline|date=October 2023}}

=== Diesel ===
Diesel locomotives are powered with a diesel engine, which generates electricity to drive traction motors. This is known as a [[diesel–electric transmission]], and is used on most larger diesels.<ref>{{Cite web|date=2014|title=Diesel Electric Locomotives|url=https://edisontechcenter.org/Dieseltrains.html|access-date=2021-11-05|website=edisontechcenter.org}}</ref> Diesel power replaced steam for a variety of reasons: diesel locomotives were less complex, far more reliable, cheaper, cleaner, easier to maintain, and more fuel efficient.<ref name="anymore" />

=== Electric ===
[[Image:SwissMGB.jpg|thumbnail|Swiss Electric locomotive at [[Brig, Switzerland]]]]Electric trains receive their current via [[overhead lines]] or through a [[Third rail|third rail electric system]], which is then used to power traction motors that drive the wheels.<ref name="electrification" /> Electric traction offers a lower cost per mile of train operation but at a higher initial cost, which can only be justified on high traffic lines. Even though the cost per mile of construction is much higher, electric traction is cheaper to operate thanks to lower maintenance and purchase costs for locomotives and equipment.<ref name="electrification" /> Compared to diesel locomotives, electric locomotives produce no direct emissions and accelerate much faster, making them better suited to passenger service, especially underground.<ref name="electrification" /><ref>{{Cite web|last=Hickman|first=Leo|date=2012-07-16|title=How green are electric trains?|url=http://www.theguardian.com/environment/blog/2012/jul/16/electric-trains-diesel-green-carbon|access-date=2021-11-05|website=The Guardian|language=en}}</ref>

=== Other types ===
[[File:Union_Pacific_third_generation_GTEL_locomotive.JPG|thumb|A [[gas turbine locomotive]] operated by the [[Union Pacific Railroad]]]]
{{See also|Alternative fuel locomotive}}
Various other types of train propulsion have been tried, some more successful than others.

In the mid 1900s, [[gas turbine locomotive]]s were developed and successfully used, though most were retired due to high fuel costs and poor reliability.<ref>{{Cite web|title=About Gas Turbine Locomotives|url=http://www.up.com/up/aboutup/special_trains/gas-turbine/index.htm|access-date=2021-11-05|website=www.up.com|language=en}}</ref>

In the 21st century, alternative fuels for locomotives are under development, due to increasing costs for diesel and a desire to reduce greenhouse gas emissions from trains. Examples include [[hydrail]] (trains powered by hydrogen fuel cells) and the use of compressed or [[liquefied natural gas]].<ref>{{Cite web|last=Clinnick|first=Robert|date=October 21, 2021|title=Worldwide hydrogen projects gain traction|url=https://www.railjournal.com/in_depth/worldwide-hydrogen-projects-gain-traction/|access-date=2021-11-07|website=International Railway Journal|language=en}}</ref><ref>{{Cite web|last=Vantuono|first=William C.|date=2021-11-01|title=CP: Green 'Gas 'n Go' Gets Grant|url=https://www.railwayage.com/mechanical/locomotives/cp-green-gas-n-go-gets-grant/|access-date=2021-11-07|website=Railway Age|language=en-US}}</ref>