Line 4 or 4 Line may refer to:
Public transport
Asia Line 4 (Chennai Metro), or Orange Line, under construction in India Line 4 (Riyadh Metro), in Saudi Arabia Yellow Line (Kolkata Metro), in India Busan Metro Line 4, a rubber-tyred metro line in Busan, South Korea Manila Light Rail Transit System Line 4, Metro Manila, Philippines MRT Line 4 (Dhaka Metro Rail), in Bangladesh Line 4 (Mumbai Metro), under early stages of construction Chūō Line (Osaka) or Chūō Line, in Japan Seoul Subway Line 4, a line across the National Capital Area, South Korea Sri Petaling Line, the fourth rapid transit line in Klang Valley, Malaysia Zhonghe–Xinlu line, a metro line in Taipei, Taiwan
China Line 4 (Beijing Subway), a subway line in Beijing Line 4 (Changchun Rail Transit), a metro line in Changchun, Jilin Line 4 (Changsha Metro), a metro line in Changsha, Hunan Line 4 (Chengdu Metro), a metro line in Chengdu, Sichuan Line 4 (Chongqing Rail Transit), a metro line in Chongqing Line 4 (Dongguan Rail Transit), a planned metro line in Dongguan, Guangdong Line 4 (Fuzhou Metro), a line under construction in Fuzhou, Fujian Line 4 (Guangzhou Metro), a metro line in Guangzhou, Guangdong Line 4 (Hangzhou Metro), a metro line in Hangzhou, Zhejiang Line 4 (Hefei Metro), a metro line in Hefei, Anhui Line 4 (Jinan Metro), a metro line in Jinan, Shandong Line 4 (Kunming Metro), a metro line in Kunming, Yunnan Line 4 (Nanchang Metro), a metro line in Nanchang, Jiangxi Line 4 (Nanjing Metro), a metro line in Nanjing, Jiangsu Line 4 (Nanning Metro), a metro line in Nanning, Guangxi Line 4 (Ningbo Rail Transit), a metro line in Ningbo, Zhejiang Line 4 (Qingdao Metro), a metro line in Qingdao, Shandong Line 4 (Shanghai Metro), a metro line in Shanghai Line 4 (Shenzhen Metro), a metro line in Shenzhen, Guangdong Line 4 (Suzhou Metro), a metro line in Suzhou, Jiangsu Line 4 (Tianjin Metro), a metro line in Tianjin Line 4 (Wuhan Metro), a metro line in Wuhan, Hubei Line 4 (Wuxi Metro), a metro line in Wuxi, Jiangsu Line 4 (Xi'an Metro), a metro line in Xi'an, Shaanxi Line 4 (Xiamen Metro), a metro line in Xiamen, Fujian Line 4 (Zhengzhou Metro), a metro line in Zhengzhou, Henan
Europe Line 4 (Athens Metro), an under construction metro line in Greece Barcelona Metro line 4, a line in Spain Rodalies Barcelona line 4, a commuter railway in Spain Line 4 (Bilbao Metro), a proposed line Line 4 (Bucharest Metro), a line in Romania Line 4 (Budapest Metro), a line in Hungary Line 4 (Madrid Metro), a line in Spain Line 4 (Milan metro), an underground rapid transit line under construction in Italy Line 4 (Moscow Metro), a metro line in Moscow, Russia Paris Metro Line 4, a line in France Paris Tramway Line 4, a tram-train line just outside the limits of Paris proper Line 4 (Saint Petersburg Metro), a metro line in Saint Petersburg, Russia U4 (Vienna U-Bahn), a line in Austria
Oceania Eastern Suburbs and Illawarra Line, coded T4, coloured navy, a train line in Sydney, New South Wales.
North America Line 4 Sheppard, a subway line in Toronto, Canada Yellow Line (Montreal Metro), formerly known as Line 4, in Canada Line 4 of the Guadalajara urban rail system, Mexico Mexico City Metro Line 4, a rapid transit line in Mexico City Mexico City Metrobús Line 4, a bus rapid transit line in Mexico City Route 4 (Baltimore), a bus route in the United States No. 4 Line (Baltimore streetcar), replaced by MTA Maryland Route 15 4 (New York City Subway service), a subway line in New York City 4 (Los Angeles Railway), streetcar lines in Los Angeles 4 Line (Sound Transit), a planned light rail line in Washington State Line 4 (O-Train), the Airport Link (Blue Line) of Ottawa's O-Train
South America Line 4 (Rio de Janeiro), a line under construction in Brazil Line 4 (São Paulo Metro), a line under construction in Brazil Santiago Metro Line 4, in Chile Santiago Metro Line 4A, in Chile
Measurement 4-line, obsolete measure in Line 4-line, 12.17x44mm ammunition or a rifle which fires it
See also 4 Train (disambiguation) List of public transport routes numbered 4