Overdrive gear is mechanism used in the many vehicles with automatic transmission to keep the vehicle with high speed with less input of energy from engine. Using this using, people can even keep the vehicle running at constant speed with cruise mode added to the vehicle. The usage of less energy mean, the engine consume less fuel to provide less output that is then enhanced by overdrive gear. As the engine consume less fuel, mean the vehicle can be more fuel efficient. When the vehicle is in overdrive gear, people will not have to give more throttle input to gain more speed, but instead it will be automatically done by overdrive gear with less power input. People should also know that acceleration rate of the vehicle will be less when it is kept in overdrive gear mode. Still people can take out the vehicle form overdrive gear mode and start the acceleration in regular mode and then switch back to overdrive gear mode when they have to maintain the constant speed on open road.