However, with increasing air traffic and the assignment of distinct flight levels to specific flights, airways, and directions of flight, it is no longer safe to climb continuously in this way, and so most flights compromise by climbing in distinct steps—a step climb—with ATC approval, in order to ensure that the aircraft is always at an appropriate altitude for traffic control. While not quite as efficient as a continuous cruise climb, step climbs are still more efficient than maintaining a single altitude throughout a flight. The step climb intervals may be 1,000 or 2,000 or 4,000 ft (300 or 610 or 1,220 m), depending on the flight level rules which apply on the particular airway being flown.