Radar control is a method of providing air traffic control services with the use of radar and Automatic Dependent Surveillance (ADS–B).
In air traffic control, the risk of aircraft colliding is managed by applying separation rules.
In airspace with a lower amount of traffic, controllers will require pilots to navigate their aircraft on published routes which have been designed to be separated from each other.
Controllers may require pilots to fly their aircraft at certain speeds or with certain minimum or maximum speeds to maintain separation between aircraft on these routes.
When the amount of traffic in a particular volume of airspace reaches a certain level, it becomes impossible to keep aircraft following set routes separated, particularly in airspace where aircraft are climbing and descending (and therefore level separation regularly cannot be maintained).