Final answer:
Greyhound Lines, Inc. and Trailways Transportation System likely preferred the broader market definition for intercity transportation including cars and flights, as it would lessen concerns from regulatory bodies regarding market concentration during their merger.
Step-by-step explanation:
When two intercity bus companies, Greyhound Lines, Inc. and Trailways Transportation System, wanted to merge, they had to consider how to define their market. The first option was to define it narrowly as "the market for intercity bus service." A broader definition included "the market for intercity transportation," which would encompass personal cars, car rentals, passenger trains, and commuter air flights.
The bus companies likely preferred the broader definition because it would demonstrate less market concentration and present them as a smaller part of the entire intercity transportation market. This would generally appear more favorable in the eyes of regulatory bodies evaluating the merger for antitrust concerns, as it would suggest the merger would not create or reinforce a dominant position in the transportation market.