Airlines potentially value very fast aircraft, because it enables the aircraft to make more flights per day, providing a higher return on investment. Also, passengers generally prefer faster, shorter-duration trips to slower, longer-duration trips, so operating faster aircraft can give an airline a competitive advantage, even to the extent that many customers will willingly pay higher fares for the benefit of saving time and/or arriving sooner. However, Concorde's high noise levels around airports, time zone issues, and insufficient speed meant that only a single return trip could be made per day, so the extra speed was not an advantage to the airline other than as a selling feature to its customers. The proposed American SSTs were intended to fly at Mach 3, partly for this reason. However, allowing for acceleration and deceleration time, a trans-Atlantic trip on a Mach 3 SST would be less than three times as fast as a Mach 1 trip.