mainline

• Main line (railway), the principal artery of a railway system
• Main line railway preservation, the practice of operating preserved trains on an operational railway network

;Bangladesh

• Main line, MRT Line 2 of Dhaka Metro Rail

;India

• Ahmedabad–Mumbai main line
• Chennai Central–Mysuru main line
• Gandhidham–Ahmedabad main line
• Howrah–Bardhaman main line
• Howrah–Chennai main line, between Chennai and Kolkata
• Howrah–Delhi main line
• New Delhi–Chennai main line

;Japan

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• Arashiyama Main Line
• Chichibu Main Line
• Chikuhō Main Line
• Chūō Main Line
• Eiden Eizan Main Line
• Fukushima Rinkai Railway Main Line
• Hakodate Main Line
• Hankyū Kōbe Main Line
• Hankyu Kyoto Main Line
• Hankyu Takarazuka Main Line
• Hanshin Main Line
• Hidaka Main Line
• Hiroden Main Line
• Hōhi Main Line
• Hokuriku Main Line
• Kagoshima Main Line
• Kansai Main Line
• Keihan Main Line
• Keikyū Main Line
• Keisei Main Line
• Kisei Main Line
• Kyūdai Main Line
• Meitetsu Nagoya Main Line
• Mizushima Main Line
• Muroran Main Line
• Nagasaki Main Line
• Nankai Main Line
• Nayoro Main Line
• Nemuro Main Line
• Nippō Main Line
• Ohmi Railway Main Line
• Ōigawa Railway Ōigawa Main Line
• Osaka Monorail Main Line
• Ōu Main Line
• Rumoi Main Line
• San'in Main Line
• Sanyo Electric Railway Main Line
• San'yō Main Line
• Sekihoku Main Line
• Senmō Main Line
• Shin'etsu Main Line
• Sōbu Main Line
• Sōtetsu Main Line
• Sōya Main Line
• Takayama Main Line
• Tōhoku Main Line
• Tōkaidō Main Line
• Toyama Chihō Railway Main Line
• Toyohashi Railroad Azumada Main Line
• Uetsu Main Line

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;Korea

• Trans-Korean Main Line

;Pakistan

• Karachi–Peshawar Line, also referred to as Main Line 1

;Philippines

• PNR North Main Line
• PNR South Main Line

;Sri Lanka

• Main Line (Sri Lanka)

;Thailand

• Chiang Mai Main Line, between Bangkok and Chiang Mai
• Ubon Ratchathani Main Line, between Ban Phachi Junction and Ubon Ratchathani

;Turkey

• Adana – Mersin Main Line

• Main Line for Europe

;Finland

• Finnish Main Line, between Helsinki and Oulu

;Germany

• Baden main line, between Baden and Constance

;Sweden

• Northern Main Line, between Gävle or Storvik and Ånge
• Southern Main Line, between Malmö and Katrineholm
• Western Main Line, between Stockholm and Gothenburg

;United Kingdom

• Brighton Main Line
• Caledonian main line
• Chatham Main Line
• Chiltern Main Line
• Cornish Main Line
• East Coast Main Line
• Great Central Main Line
• Great Eastern Main Line
• Great Western Main Line
• Highland Main Line
• Main Line Preservation Group, an organisation that eventually became the Great Central Railway heritage railway
• Mainline Freight, a defunct UK railfreight company
• Midland Main Line
• Midland Mainline (train operating company), a defunct UK train-operating company
• North British Railway Main Line
• Penrhyn Main Line class, three narrow-gauge steam locomotives built for the Penrhyn Quarry Railway
• South Eastern Main Line
• South Humberside Main Line, between Doncaster and Cleethorpes
• South Wales Main Line
• South West Main Line
• West Anglia Main Line
• West Coast Main Line
• Wessex Main Line

;United States

• Cape Main Line, in Cape Cod, Massachusetts
• IRT Manhattan Main Line, in New York City
• Main Line (Atlantic Coast Line Railroad), now the CSX A Line
• Main Line (Seaboard Air Line Railroad), now the CSX S Line
• Main Line (Columbus to Chicago), a Pennsylvania Railroad line in Ohio, Indiana, and Illinois
• Main Line (Columbus to Indianapolis via Bradford), a Pennsylvania Railroad line in Ohio
• Main Line (Pennsylvania Railroad), between Philadelphia and Pittsburgh, Pennsylvania
• Main Line (Long Island Rail Road), between Long Island City and Greenport, New York
• Main Line (New York to Hoffmans), a nickname for the CSX Hudson Subdivision
• Main Line (NJ Transit), formerly part of the Erie Railroad, between Hoboken and Suffern, New Jersey
• Main Line (Pittsburgh to St. Louis), a Pennsylvania Railroad line between Ohio and Illinois
• Main Line (Reading Company), the former Reading main line between Philadelphia and Pottsville, Pennsylvania
• Main Line of Mid-America, a nickname of the former Illinois Central Railroad
• Main Line Subdivision, owned by CSX Transportation in Kentucky and Tennessee
• Main Street Line (MATA Trolley), a streetcar line in Memphis, Tennessee
• Metropolitan main line, a former rapid transit line in Chicago, Illinois
• North Side main line, a rapid transit line in Chicago, Illinois
• Old Main Line Subdivision, between Relay (outside Baltimore) and Point of Rocks, Maryland
• Park Avenue main line, the former New York Central Railroad (now Metro-North Railroad) from Grand Central Terminal in Manhattan to Mott Haven Junction in the South Bronx
• Philadelphia Main Line
• Philadelphia to Harrisburg Main Line, part of the Pennsylvania Railroad Main Line now owned by Amtrak
• Philadelphia-to-Washington Main Line
• RF&P Subdivision, former Richmond, Fredericksburg, & Potomac (RF&P) Main Line
• SEPTA Main Line, between West Philadelphia and Lansdale, Pennsylvania
• South Side Main Line (Chicago Transit Authority), in Chicago, Illinois
• Washington to Atlanta Main Line, owned by Norfolk Southern Railway

;Australia

• Main Line railway, Queensland
• South Line, Tasmania, Australia, also called the Main Line
• Tasmanian Main Line Company, a privately-owned railway that existed from 1872 to 1890

;New Zealand

• Canterbury Interior Main Line, a proposed railway on the South Island

• Mainline (aeronautics), an airline carrier's non-regional service
• Main Line of Public Works, a package of legislation establishing freight transport between Philadelphia and Pittsburgh
• A toll road system where all vehicles stop at various locations on the highway to pay a toll
• BCN Main Line (Birmingham Canal Navigations Main Line), a canal between Birmingham and Wolverhampton, England
• Ford Mainline, a car model
• South Yorkshire Transport, a large bus operator in South Yorkshire, England which was renamed "Mainline" in 1993

• McKenna Mendelson Mainline, a seminal Canadian blues band
• "Mainline", a song by KISS on their 1974 album Hotter Than Hell
• "Mainline", a 1979 disco song by Black Ivory
• Mainline, a 2014 album by Australian hip-hop collective One Day.

• Main Line Broadcasting, a defunct American media company
• Main Line Health, a not-for-profit health system in Philadelphia, Pennsylvania
• Mainline Corporation, former Australian construction company
• Mainline Railways, a model railway brand now owned by Bachmann

• BitTorrent (software), nicknamed mainline by developers denoting its official origins
• Mainline Linux, the Git repository of Linus Torvalds
• Trunk or mainline, the primary branch of a software project

• Fork (software development) – a software development edition that is not part of the "Mainline" version

• Main line, a primary variation in chess
• Main line (political) (Mainlinie), a historical and political boundary between Northern and Southern Germany, roughly following the River Main

• Mainline Drive-In, a drive-in theatre in Gepps Cross, South Australia
• Mainline Protestant, a group of Christian church denominations
• "Mainlining," a slang term for intravenous drug use
• Philadelphia Main Line, a collection of suburbs of Philadelphia, Pennsylvania

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• {{in title|plural=yes|main line}}
• {{in title|plural=yes}}
• Central line (disambiguation)
• Mainliner (disambiguation)
• Old Main Line (disambiguation)
• Trunkline (disambiguation)

{{disambiguation}}