The R4 41st Ave (designated the 91 B-Line during planning stages) is an express bus route with bus rapid transit elements in Metro Vancouver, British Columbia, Canada.

Part of TransLink's RapidBus network, it replaced the 43 Express that travelled along 41st Avenue, a major east–west route that connects the University of British Columbia (UBC) to the SkyTrain system's Oakridge–41st Avenue station on the Canada Line and Joyce–Collingwood station on the Expo Line.

Nevertheless, the 43 Express was included as a main transit connection in a plan released following the opening of the Canada Line, indicating the importance of the route within the TransLink network.

[5] On November 23, 2016, the Mayors' Council and TransLink's board of directors approved the first phase of the 10-Year Vision, which included provisions for new B-Line routes (including the 41st Avenue B-Line) which began service on January 6, 2020.

[1][6] On July 23, 2019, the route was officially rebranded the R4 41st Ave.[7] The R4 travels mainly on 41st Avenue in Vancouver, and also along Joyce Street, Southwest Marine Drive, West 16th Avenue, and Wesbrook Mall.