Its main purpose is to provide service to the upper Northwest side via Wisconsin Avenue NW.

In 2008, WMATA launched a study on the Pennsylvania Avenue line to improve services and to reduce delays and bus bunchings.

[2] Route 31 was introduced on June 29, 2008, dubbed as a "neighborhood connector" as part of an overhaul of the busy Pennsylvania Avenue Line.

[3] As part of proposals from 2013 to simplify the Wisconsin Avenue Line again,[4] route 33 was introduced on August 24, 2014 to replace the 32 and 36 portion along Wisconsin Avenue and to provide extra service to the 31, and the newly introduced Friendship Heights–Southeast Line or routes 30N and 30S.

[5][6] During the COVID-19 pandemic, routes 31 and 33 operated on their Saturday supplemental schedule during the weekdays beginning on March 16, 2020.