You might already unknowingly use co-terminals in trip planning. It is worthwhile to check co-terminal flight options, as it will often provide you with better flights at lower prices.
Below is an excerpt from my book, Winning the Airfare Game, published in 2001.
Co-Terminals
Using co-terminals[1] can result in lower airfares because airlines do not typically charge extra to use them. Instead, airlines determine the price of a co-terminal flight by averaging the fare to each airport. An example co-terminal flight is to Miami and back from Ft. Lauderdale. If the Miami flight costs $300 and the Ft. Lauderdale flight costs $320, the airline charges $310 for the co-terminal flight.
One advantage of using co-terminals is that you can select the best flights for each airport. In the above sample trip, assume that flights to Ft. Lauderdale are convenient but return flights are not. The opposite is true for Miami—great return flights but inconvenient flights there. The solution is a co-terminal flight, to Ft. Lauderdale and back from Miami.
The days, times, routings, or upgrade possibilities may be more convenient for one route than another. Perhaps flights to and from Miami are on Monday, Wednesday, and Friday, while flights to and from Ft. Lauderdale are on Tuesday, Thursday, and Saturday. Maybe all flights from Miami on the desired return date have connections while there is a non‑stop flight from Ft. Lauderdale. Checking flights from each co-terminal allows you to get lower fares and select the most convenient flights.
A disadvantage of co-terminal flights is arranging transportation to the other airport. It may be a simple matter or a major hassle. For example, rates are higher for rental cars not returned to the pickup location.
[1] Co-terminals – airports in the same city or metropolitan area. Examples include Miami & Ft. Lauderdale, San Francisco & Oakland, and Baltimore/Dulles/National.
§§§
Do you or have you used co-terminals?
See also Travel Myth Busted: Lowest Airfare is Always Found {Here}