A two speed transmission and belt drive system utilizing the transmission. The two speed transmission comprises a planetary gear train comprising an input pulley connected to an input carrier, and a sun gear and a ring gear. The input carrier also comprises a plurality of planetary gears disposed between the sun gear and the ring gear. The sun gear is engaged with an electromagnetic brake member. The ring gear is engaged with an output pulley. A one-way clutch is disposed between the input carrier and the output shaft. The brake member is engaged at engine idle and is disengaged at engine speeds above idle. When the brake member is engaged the sun gear does not rotate, thereby driving the ring gear and output pulley at a greater speed than the input pulley. An accessory pulley operates with the transmission output pulley resulting in an accessory speed that is proportional to an engine speed at idle. At engine speeds above idle the transmission is disengaged and the output pulley to accessory pulley ratio drives the belt driven accessory at a speed less then an engine speed. An accessory can also be directly connected to the output shaft in conjunction with the output pulley. The transmission can be used with a motor generator system by providing a speed reducing unit disposed between an engine and the motor generator.