Editing Multiple unit (section)

==Design==
Most MUs are powered either by [[traction motors]], receiving their power through a [[Third rail electric system|third rail]] or [[overhead lines|overhead wire]] ([[electric multiple unit|EMU]]), or by a [[diesel engine]] ([[Diesel multiple unit|DMU]]) driving a generator producing electricity to drive traction motors.

A MU has the same power and traction components as a [[locomotive]], but instead of the components being concentrated in one car, they are spread throughout the cars that make up the unit. In many cases these cars can only propel themselves when they are part of the unit, so they are semi-permanently coupled. For example, in a DMU one car might carry the [[prime mover (locomotive)|prime mover]] and [[traction motor]]s, and another the engine for [[head-end power]] generation; an EMU might have one car carry the [[Pantograph (rail)|pantograph]] and [[transformer]], and another car carry the traction motors.

MU cars can be a motor or trailer car, it is not necessary for every one to be motorized. Trailer cars can contain supplementary equipment such as air compressors, batteries, etc.; they may also be fitted with a driving cab.

In most cases, MU trains can only be driven/controlled from dedicated cab cars. However, in some MU trains, every car is equipped with a driving console, and other controls necessary to operate the train, therefore every car can be used as a cab car whether it is motorised or not, if on the end of the train. An example of this arrangement is the [[NJ Transit]] Arrows.

=== Weight reduction ===  
An advantage of multiple unit trains is that they can be engineered to be lighter than [[locomotive]]-hauled trains with separate carriages, using [[lightweighting]] techniques to reduce energy use, track wear, and operating costs.<ref>{{cite web |title=Around the Bay Rail Study |url=https://docslib.org/doc/4837599/3-0-diesel-multiple-unit-assessment |website=Docslib |access-date=20 January 2025 |pages=3-1/28 |language=en}}</ref><ref>{{cite web |last1=Middleton |first1=B. |title=Economic viability of diesel light rail cars. |url=https://trid.trb.org/view/477353 |access-date=20 January 2025 |date=August 1997}}</ref> The term "light-weight train" was first used in the 1930s,<ref name="DLWT1934">{{cite book |last1=Eksergian |first1=R. |title=The Design of Light-Weight Trains |date=10 February 2023 |pages=667–701 |url=https://asmedigitalcollection.asme.org/fluidsengineering/article-abstract/56/7/667/1157761/The-Design-of-Light-Weight-Trains?redirectedFrom=PDF |access-date=3 April 2025}}</ref> with early designs such as the 1934 ''[[M-10000]]'' and ''[[Pioneer Zephyr]]'' in the United States, and Germany’s 1932 ''[[Flying Hamburger]]''.<ref name="ICC1936">{{cite book |title=New Types of Light Weight Passenger Trains: Statement No. 3639. File No. 68-E-4. |date=1936 |publisher=Interstate Commerce Commission |url=https://books.google.com/books?id=ttvNAAAAMAAJ |access-date=1 April 2025 |language=en}}</ref>

Modern light-weight multiple units typically use fewer [[bogies]] and distribute [[traction (engineering)|traction]] equipment across the train, improving [[energy efficiency in transport|efficiency]] and axle loading.<ref name="MDIPM">{{cite book |last1=Fuchs |first1=Christoph |last2=Golenhofen |first2=Franziska |title=Mastering Disruption and Innovation in Product Management: Connecting the Dots |date=7 September 2018 |publisher=Springer |isbn=978-3-319-93512-6 |page=45 |url=https://books.google.com/books?id=41ptDwAAQBAJ |access-date=1 April 2025 |language=en}}</ref> However, they require particular design attention for [[bridge]] loading and [[crosswind]] safety,<ref name="LCA&ACE">{{cite book |last1=Caspeele |first1=Robby |last2=Taerwe |first2=Luc |last3=Frangopol |first3=Dan M. |title=Life Cycle Analysis and Assessment in Civil Engineering: Towards an Integrated Vision: Proceedings of the Sixth International Symposium on Life-Cycle Civil Engineering |date=15 October 2018 |publisher=CRC Press |isbn=978-1-351-85756-7 |url=https://books.google.com/books?id=ECB0DwAAQBAJ |access-date=1 April 2025 |language=en}}</ref><ref name="TSCC1966">{{cite book |last1=Chilton |first1=E. G. |title=Rail gauge and rapid-transit train stability |date=December 1966 |pages=135–145 |url=https://ieeexplore.ieee.org/document/6593097 |access-date=3 April 2025}}</ref> and often include [[noise, vibration, and harshness|noise and vibration]] mitigation systems.<ref name="IFAC1999">{{cite book |last1=Persson |first1=Per |last2=Lago |first2=Thomas L. |last3=Claesson |first3=Ingvar |title=Active vibration reduction in a light weight high speed train bogie |date=1 July 1999 |pages=8764–8768 |url=https://www.sciencedirect.com/science/article/pii/S1474667017574959 |access-date=3 April 2025}}</ref>

Examples from the 21st century include the lightweight ''[[Talgo]]'' sets used in [[Spain]] and exported to [[Germany]] and [[Denmark]],<ref name="RS2024">{{cite web |last1=Batrak |first1=Oleksandr |title=Talgo Unveils New Danish Passenger Car and German ICE L Locomotive at InnoTrans 2024 |url=https://www.railway.supply/en/talgo-unveils-new-danish-passenger-car-and-german-ice-l-locomotive-at-innotrans-2024/ |website=Railway Supply |access-date=1 April 2025 |date=24 September 2024}}</ref> India’s modern ''[[Vande Bharat Express]]'' units,<ref name="MRN2023">{{cite web |title=Alstom And Medha-Stadler Consortium Bid To Make100 Lightweight Vande Bharat Train |url=https://metrorailnews.in/alstom-and-medha-stadler-consortium-bid-to-make100-lightweight-vande-bharat-train/ |publisher=Metro Rail News |access-date=3 April 2025 |date=25 February 2023}}</ref> and the upcoming ''TELLi'' fleet for [[SNCF]] regional lines in [[France]].<ref name="SNCF">{{cite web |title=Revitalizing rural rail lines with TELLi |url=https://www.groupe-sncf.com/en/innovation/local-mobility/telli |website=SNCF Group |access-date=20 January 2025 |language=en |date=12 March 2024}}</ref>