DETROIT --- Toyota Motor Sales U.S.A. unveiled its new 50-mile-per-gallon rated Prius hybrid vehicle Jan. 12 at the 2009 North American International Auto show. 

The midsize third-generation 2010 Prius will offer even better mileage ratings, Toyota said, in addition to such available features as a moonroof with solar panels, four driving modes, Intelligent Parking Assist (IPA) and steering wheel touch controls that display on the instrument panel.

The first-generation Prius entered the market in 1997 as the first mass-produced hybrid.  The company's Hybrid Synergy Drive System was introduced in 2004 on the second-generation Prius. Since then, more than 670,000 have been sold in the U.S.

The first-generation Prius, which was rated 41 EPA combined mpg, was replaced by the current model, which is EPA rated at 46 mpg, combined city/highway. Using a combination of technologies, fuel efficiency was increased to an estimated 50 miles per gallon for the new Prius.

A larger and more powerful 1.8-liter Atkinson-cycle, four-cylinder engine will power the new Prius. The larger engine actually helps improve highway mileage. By making more torque, the new engine can run at lower average rpm on the highway. When operating at lower rpm, the new engine uses less fuel. Mileage is especially improved in cold-start conditions and at higher speeds.

Use of an electric water pump and a new exhaust gas recirculation (EGR) system also contribute to the engine’s efficiency, Toyota said. The 1.8-liter Prius engine is the first Toyota power plant that requires no belts under the hood for better fuel economy and less potential maintenance.

A display panel that monitors fuel and energy consumption is standard. It provides feedback on the Prius' efficiency using three different displays to help the driver acquire economical driving habits.

The Hybrid Synergy Drive system in the 2010 Prius is 90 percent newly-developed with improvements over previous models, Toyota said. The transaxle is lighter in weight and reduces torque losses by as much as 20 percent compared to the previous model. The inverter, which converts direct current to alternating current, has a new direct cooling system to reduce size and weight. Taken together, the inverter, motor and transaxle are smaller and 20 percent lighter.

A newly developed electronically controlled regenerative braking system has been adopted, with control logic optimized to enhance regeneration.

The new Prius will offer three alternative driving modes. EV-Drive Mode allows driving on battery power alone at low speeds for about a mile, if conditions permit. There is also a Power Mode, which increases sensitivity to throttle input for a sportier feel, and an Eco Mode, which helps the driver achieve their best mileage.