A "Mass Transportation's Directory" such as this, is among the very few records of the existence of many of these bus lines. Only a few of these lines were ever listed in the "Russell's Official National Motor Coach Guide", or ever reported on in the "Motor Coach Age" magazine. Many of these lines came and went, and the listings in a "Mass Transportation's Directory" for a different year presumably will have a number of differences.
Included are bus lines which have been identified as "suburban", along with bus lines generally operating in only one or just a few counties. For the purposes of these Web pages, bus lines operating over longer distances are considered as "intercity". And nearly all "intercity" bus companies were included in the Russell's Guide.
For these Web pages for each state, such classifications of bus companies is often arbitrary. For each state, bus lines are generally grouped geographically. Because of differences in states, including the evolution of such bus lines in each state, differences exist how bus lines are classified in each state.
Not included are certain longer distance intercity bus providers also providing suburban or commuter service. Some lines may be omitted, due to incompleteness or inconsistencies with available data.
Many of these bus lines operated beyond the regions which eventually approved creation of publicly owned transit agencies. As a result, service was usually eventually discontinued.