Prior to its use in 2008, the no. 54 designation had been used for bus service along Liberty and Milford Mill Roads from 1948 to 1955. With this exception, other designations were used for service along all portions of the current route.
In 1916, the no. 5 streetcar started operating along the Park Heights Avenue corridor. This route originally operated to Emory Grove in Reisterstown, but later would be shortened in several steps and gradually replaced by various buses. It was truncated to Pikesville in 1932, Manhattan Avenue (near Northern Parkway) in 1938, and ultimately saw its end as a streetcar in 1948.
In 1948, the no. 5 streetcar was converted into a bus operation. The line was identified as the no. 5/7 line from 1948 to 1959, and was then split into two separate lines, identified as the no. 5 and 7. From this day until 1984, Route 5 provided service at all times along Park Heights Avenue from Slade Avenue to downtown Baltimore and beyond. Route 5 continued to provide service on Park Heights Avenue when the Metro was not operating until 2001, when full-time Sunday Metro service was introduced on Route M-3.
The original no. 54 line provided service from 1948 to 1955 along Liberty and Milford Mill Roads. In 1955, the now-defunct Route 28 absorbed this service. Route 28 provided this service full-time until 1984, when various Metro connection services replaced Route 28 service during Metro's hours of operation. Route 28 continued to operate 7 days a week until 1996, when the line was absorbed by Routes 5 and 27. Sunday service on Route 28 continued to operate until 2001, when Sunday Metro connection bus service was introduced.