"D" Position Overdrive Switch: On
WARNING: This page is about a different car, the 2009 Nissan Sentra. However, it is still accessible from the selected car via links, so may be relevant.
Gear ratio increases in general by limiting gear range on the HIGH side of the gear ratio, and this arrows the generation of the constant strong driving force.
Courtesy of NISSAN MOTOR CO., U.S.A.