The Toyota Prius is a four-door, five-passenger subcompact hybrid hatchback. The Toyota Prius is the most fuel-efficient vehicle sold in the United States. The current generation, introduced in 2004, has a drive train that is composed of a hybrid gasoline-electric system which can operate off of the battery exclusively at low speeds or when stopped. It can also use the electric motor and gasoline motor simultaneously, greatly reducing the amount of fuel needed during normal operation.

The gasoline engine in the Prius uses a form of internal combustion called the Atkinson cycle, which differs from standard automotive engines in that it is designed more for fuel economy than performance. This 76 horsepower, 4 cylinder engine has two roles: charging the batteries that power the electric motor, and also powering the vehicle itself, depending on the driving situation. The batteries are additionally charged via a regenerative braking system, which uses generators mounted in each wheel to convert rotational energy into electricity. The batteries in the Prius are made of nickel-metal hydride, and in the 2008 model are connected to an electric motor generating 67 horsepower and 295 lb-ft of torque. When working in tandem, the hybrid system provides 110 useable horsepower to the driver.

The Prius manages to maintain its 46 mile per gallon combined fuel mileage in large part by using a computer system to control a series of driving modes. When the vehicle is stopped, the gasoline engine is shut off completely, and does not re-start until vehicle speeds reach a point where the electric motor requires additional power. The relatively weak gasoline engine is assisted by the electric motor during rapid acceleration or hill climbing, allowing for reduced fuel consumption while still providing a safe and useful amount of performance. Aerodynamics also play a key role, and the Prius has the lowest drag coefficient of any commercially available vehicle. This allows it to slice through the air at highway speeds with a minimum of wind resistance. Finally, lightweight materials are used throughout the vehicle in order to keep the overall mass of the Prius as low as possible. The automobile uses a continuously variable transmission to direct power from both motors to the front wheels.

The current Prius is available as a 4 door hatchback, and differs in several respects from previous versions of the car. Air conditioning is now powered solely by electricity, which further reduces fuel consumption. In addition, the vehicle is now also outfitted with stability control and a navigation system. In an attempt to dress up the Prius and make it more appealing to a younger demographic, sportier wheels along with an exterior appearance package and HID headlights are now optional from Toyota.

While the Prius has been touted as an environmentally-friendly alternative to traditional automobiles, there is some controversy regarding the overall ecological impact of the vehicle. This is related to the energy required to manufacture the batteries, as well as the fact that several of the more exotic materials used in the vehicle’s construction also require an energy-intensive process to produce. With regards to gas mileage, in the European market, there are certain diesel vehicles which can equal the fuel economy of the Prius without requiring a hybrid drive train. The 2009 Toyota Prius is a carryover from 2008. There are two different trim levels available for the Prius, the base and the Touring. Both employ the same Hybrid Synergy Drive that has made the vehicle a household name. Combining a 1.5 liter, 4-cylinder engine with an electric generator, the system outputs a total of 110 horsepower. Torque from the gasoline engine is rated at 82 lb-ft, with the electric motor capable of producing 295 lb-ft. Fuel economy for the 2009 Prius is a stellar 48 miles per gallon around town and 45 miles per gallon during highway cruising.