For airline city-pairs, the Bureau of Transportation Statistics (BTS) selected only nonstop flights. Since ground transportation modes operate linear routes serving many intermediate cities, BTS selected direct rail or bus service whether or not intermediate stops were scheduled. In the event that direct service was not available from the rail or bus carriers, BTS used the single fastest connecting schedule as the basis for theanalysis. In some city-pairs, rail/bus connections sponsored by Amtrak (“Amtrak Thruway”) were considered as rail service except where the bus portion represented more than half of the travel miles.
The number of rail and bus city-pairs is lower than the number of air city-pairs because the air analysis in some cases considered multiple airports in the same city. Also, somerail city-pairs were not used because the only possible routing is so impractical that service is effectively not available. For example, a traveler using Amtrak for the 300-mile trip between Pittsburgh and Cincinnati would have to travel 800 miles via Chicago with a 12-hour layover.
While the city-pairs in the study encompass many of the nation’s major intercity travel markets, the lack of publicly available data on specific city-pair traffic volumes for all three modes prevented BTS from constructing reliable samples of markets to represent the entirety of each mode. Therefore, the results of this study cannot be generalized for the industry as a whole and are applicable only to the markets considered.
BTS recognizes that there is variability in scheduled travel times, especially for airline schedules, on both a month-to-month and year-to-year basis. The lack of bus and rail data for prior years in an electronic format precluded current consideration of additional time periods in this analysis. BTS will analyze additional time periods and look at the variability of scheduled travel times for all three modes in future work on this subject.