In 1966, the Detroit Department of Street Railways (DSR) attempted to implement a new "bus-by-number only" system to identify its bus routes. However, a combination "route-number & route-name" identification system was used first, and began to first appear on DSR buses upon the arrival of a fleet of new GM model TDH–5303 coaches (#2401-2500), which were delivered in September of 1966. It was originally intended that eventually the street route names were to be removed, leaving only numbers. However, to this day, both the route names and the route numbers are still displayed on Detroit city buses.

The new DSR route numbering system, for the most part, arranged the bus route names in alphabetical order, assigning even route numbers to identify east-west bus routes and odd numbers to north-south routes. This would account for the missing routes numbers and gaps found throughout the listing. (see chart below)

The one major exception to the alphabetical numbering sequence would be whenever U.S. Highway route numbers were used to identify those bus lines that traveled along major U.S. highway routes. For example, the Woodward line was identified as route #10 WOODWARD and the Michigan line as route #12 MICHIGAN, because those were their then corresponding U.S. Highway route designation numbers.

The following is a listing of the DSR bus route numbers in effect during the later DSR years, before the DDOT change-over. The chart can also allow visitors to our site an opportunity to glimpse at the level of service available to Detroiters during the early 1970s. Since the DSR did not assign different route numbers to its express routes, available express service will be noted under the "Express" column.