DETROIT – Toyota Motor Corp. stages the world debut of its third-generation Prius hybrid-electric vehicle at the 2009 North American International Auto Show here.

The auto maker estimates the car’s Environmental Protection Agency fuel-economy rating will be 50 mpg (4.7 L/100 km). That’s less than the wild numbers rumored but more than previous models.

The first-generation Prius had an EPA rating of 41 mpg (5.7 L/100 km), while the second-generation was improved to 46 mpg (5.1 L/100 km).

The Prius gets a Toyota-first beltless engine, a 1.8L 4-cyl. Although higher in displacement than the outgoing model’s 1.5L 4-cyl., the auto maker says the larger mill helps improve the car’s highway fuel efficiency through increased torque, allowing the engine to run at lower, fuel-sipping rpms.

The combined hybrid system kicks out 134 hp, up from 110 hp in the outgoing Prius. The 1.8L engine makes 98 hp and 105 lb.-ft. (142 Nm) of torque, while the electric motor produces another 80 hp and 153 lb.-ft. (207 Nm) of torque.

Toyota’s Hybrid Synergy Drive system in the ’10 Prius is 90% newly developed, with a lighter-weight transaxle that cuts torque losses as much as 20%. An inverter with a direct cooling system reduces size and weight, and there is a new electronically controlled regenerative-braking system with optimized control logic.

The ’10 Prius boasts three drive modes: EV-Drive, Power and Eco. The car in EV-Drive mode can run solely on battery power for about 1 mile (0.6 km) at low speeds, Toyota says. Power mode “increases sensitivity to throttle input for a sportier feel,” and Eco mode “helps the driver achieve their best mileage.”

In other Toyota HEVs, Eco mode reduces the intensity of the air-conditioning system, lessening fuel consumption.

The ’10 Prius offers an optional sliding-glass moonroof with solar panels, which reduces the need for air-conditioning by powering a solar-ventilation system. The system uses an electrically powered air-circulation fan that doesn’t draw engine power and keeps the car’s interior air temperature from rising when the vehicle is parked.

The HEV’s AC system can be operated by remote control and function on battery power alone, a world-first, the auto maker claims.

While the ’10 Prius’ platform is classified as new by Toyota, the car’s wheelbase remains the same at 106.3 ins. (270 cm). Length is increased 0.6 ins. (1.5 cm) due in part to a front cowl that is pushed forward.

The exterior “triangle” shape of the Prius remains intact, but designers have sharpened the corners and tweaked the car’s roof profile by moving the high point 3.9 ins. (9.9 cm) rearward. The change “emphasizes the wedge shape” design and improves rear headroom and aerodynamics.

The ’10 Prius claims a world-best 0.25 drag coefficient. Toyota says the car spent more time testing in a wind tunnel than any of the auto maker’s models ever. The Cd value of the outgoing Prius is 0.26.

The Prius’ aerodynamics also are improved by focusing on the movement of airflow under the car. “Engineers made changes to the shape of the fender liner, front surface of the underfloor and added a fin at the rear floor cover to increase linear stability,” the auto maker says.

The new model’s suspension retains front struts and a rear intermediate beam design. However, Toyota says an improvement in the stabilizer layout and caster angle and the way it tunes the bushing characteristics provide for an overall improvement in handling stability from second- to third-generation.

The ’10 Prius has a longer, wider cargo area than its predecessor, due to a changed battery-cooling unit layout. Contoured front seats allow for more rear legroom. Additionally, the shift lever has been relocated from the steering column to the center console, which protrudes outward into the cabin, leaving a large storage space below the lever.

A world-first Touch Tracer system is touted by Toyota as improving driver concentration. Touch sensors on the steering-wheel mounted switches bring up a duplicate image of the switches on the instrument panel, keeping driver eye movement to a minimum.

As with the new Lexus HS 250h HEV, Toyota says it used plant-derived, carbon-neutral “ecological plastics” in the Prius’ interior, including the seat cushion foam, cowl side trim, inner and outer scuff plates and deck-trim cover.

Having been accused of a non-environmentally friendly manufacturing footprint with the Prius, Toyota says it will build the third-generation using processes “that reduce pollution in every stage of vehicle life, from production and driving through to disposal.”

The ’10 Prius hybrid is due in U.S. showrooms by late spring.