Transbrake

In drag racing, a transbrake is a setup installed in automatic transmissions which places the transmission in first and reverse gears at the same time, effectively "braking" the transmission. With the transmission locked in this manner, the engine can be accelerated to a certain RPM in preparation for launch and the racer doesn't need to worry about the car creeping forward. A split second before the green light illuminates on the Tree the transbrake is released (either automatically by a delay box or manually by the driver) and the car launches forward, its engine already at the beginning of its powerband and the transmission is already in gear.