Which function does the overdrive gear serve in an automatic transmission?

The overdrive gear in an automatic transmission primarily serves to improve fuel efficiency at highway speeds. When the vehicle is cruising at higher speeds, engaging the overdrive allows the engine to operate at a lower RPM relative to the vehicle speed. This results in less engine strain and reduced fuel consumption.

Since the engine does not have to work as hard in overdrive, it not only conserves fuel but also reduces wear on engine components. This functionality is essential for long-distance travel, where maintaining efficiency is a priority.

In comparison, other functions mentioned, such as enhancing engine power at low speeds or increasing torque when towing, focus on different aspects of vehicle performance at various driving conditions, which do not relate to the primary role of the overdrive gear in promoting fuel economy during highway driving.