Anticipated Separation: Departure / Departure

Takeoff clearance needs not be withheld until prescribed separation exists if there is a reasonable assurance it will exist when the aircraft starts takeoff roll.

The first aircraft must be airborne before the second aircraft commences the take-off roll (in addition, aircraft type should be taken into account).

For example, if aircraft A (B737) is above 100knts GS and aircraft B (A320) is holding short, simply clear aircraft B for takeoff. No need for a line up and wait instruction.