The Oxon Hill–Suitland Line, designated Routes D12 & D14, are daily bus routes operated by the Washington Metropolitan Area Transit Authority between Southern Avenue station and Suitland station of the Green Line of the Washington Metro.

The line formally operated out of Southern Avenue garage on weekdays and Shepherd Parkway on weekends.

[5] During the PM rush, passengers can get on and off northbound buses going to Federal Center SW at any bus stop in Maryland and the District of Columbia with southbound restrictions not changing.

[6] In 2010 during WMATA's FY2011 budget, WMATA proposed to divert routes D13 and D14 into Oxon Hill Park & Ride Lot off Oxon Hill Road just west of Indian Head Highway in order to create a transfer connection between those routes and the NH1, which serves National Harbor.

This would provide closer connections to National Harbor for passengers instead of having to take the Green Line to Branch Avenue station.

This prevents buses from turning left from Indian Head Hwy - MD 210 onto Livingston Road.

A temporary time transfer was also implemented for affected passengers at closed bus stops westbound.

[13] In February 2021 during the FY2022 budget, WMATA proposed to eliminate Routes D13 and D14, and propose to extend the D12 to National Harbor to replace the NH1 and eliminate service between Southern Avenue station and Livingston Road & Oxon Hill Road if it did not receive federal funding.

[15] On September 5, 2021, all Route D13 service was renamed to the D14 while D14 service along Livingston Road, Livingston Terrace, Marcy Avenue, Deal Drive, Kennebec Street, Glassmanor Drive, Irvington Street, and Audrey Lane in Glassmanor was eliminated.