15 streetcar started operating along the western portion of this route as far west as Franklintown Road.

6 Streetcar (where service is currently provided by bus route 35), the West Arlington Jerkwater which operated briefly in 1930 (where service is currently provided by bus route 44),[3] the Dundalk Short Line, which operated from 1930 to 1936, and the Point Breeze streetcar/bus, which operated from 1940 to 1948, which was reduced to a shuttle in 1948 before being absorbed by other services.

[4] The line saw later expansions on the west side while communities developed in Edmondson Village, Westview, and Woodlawn, and was eventually extended to Rolling Road and Security Boulevard.

In October 2005, as part of the Greater Baltimore Bus Initiative, a comprehensive overhaul plan, Route 20 underwent the following changes: On 22 February 2015, service was cut to run between Security Square Mall and City Hall, with short turns at Edmonsdon Village [6] as part of the first phase implementation of the Bus Network Improvement Project.

[7] In Every Secret Thing By Laura Lippman, the narrator describes her plans to take the bus to St. Agnes Lane near U.S. 40, where Route 20 operates.