D Line

D Line may refer to:

Transportation

 * Line D (Buenos Aires Underground), an underground line in Buenos Aires, Argentina
 * D Line (Los Angeles Metro), a rapid transit line in Los Angeles County, California
 * Line D (Prague Metro), a subway route under construction in Prague, the Czech Republic
 * Line D (Rome Metro), potential line of the Rome Metro system
 * D Line (RTD), a light rail line in Denver
 * Green Line D branch, a light rail line in Boston
 * D (New York City Subway service), a subway route in New York
 * RapidRide D Line, a bus route in Seattle, Washington, United States
 * Metro D Line (Minnesota), a bus rapid transit line in Minneapolis, Minnesota, United States
 * D (Los Angeles Railway), a former streetcar line in Los Angeles, California

Other uses

 * D-line, Port Harcourt, a neighborhood in Port Harcourt, Nigeria
 * D-line (IRC), a command in IRCd
 * D-line, a spectral line of the Fraunhofer lines