The Toyota Prius is a full hybrid electric automobile developed by Toyota. Initially offered as a 4-door sedan, it has been produced only as a 5-door hatchback since 2003. The 2016 model year Prius Eco ranks as the all-time most fuel efficient gasoline-powered car. The Prius is sold in over 90 markets, with Japan and the United States being its largest markets. Global cumulative Prius lift-back sales reached the milestone 1 million vehicle mark in May 2008, 2 million in September 2010, and passed the 3 million mark in June 2013. The production version of the Prius plug-in hybrid was released in 2012. The Prius family totaled global cumulative sales of 6.1 million units in January 2017, representing 61% of the 10 million hybrids sold worldwide by Toyota since 1997. The fourth generation Prius was first shown during September 2015 in Las Vegas, and was released for retail customers in Japan in December 2015. Toyota expected to sell 12,000 fourth generation Prius cars a month in Japan, and to reach annual sales between 300,000 and 350,000 units. In August 2013, Toyota Managing Officer announced some of the improvements and key features of the next generation Prius. The next Prius is the first vehicle to use the Toyota New Global Architecture modular platform, which provides a lower center of gravity and increased structural rigidity. These features, along with other improvements allow for gains in ride-and-handling, agility and aerodynamics. The improved aerodynamics contribute to an all-new exterior design, which includes a roomier interior. He also explained that the next-generation Prius plug-in hybrid, the Prius Prime, was developed in parallel with the standard Prius model. The fourth generation Prius has stirred controversy over the style and cohesion of its exterior design, with analysis from critics contending that the excessively angular headlamps and unnecessary creases in the bodywork has created a haphazard design, that falls into the trap of equating aggressiveness with sportiness. The fourth-generation Prius is designed to deliver significantly improved fuel economy in a more compact package that is lighter in weight and lower in cost. These objectives were achieved through the development of a new generation of power-trains with significant advances in battery, electric motor and gasoline engine technologies. It features improved batteries with higher energy density, smaller electric motors, with higher power density than the previous Prius motors, and the gasoline engine features a thermal efficiency greater than 40% ,that of the third-generation Prius is 38.5%. The Prius fuel economy has improved on average by about 10% each generation, and Toyota has set the challenge to continue to improve at this rate. Under the Japanese JC08 cycle test, Toyota expects the fourth generation Prius to achieve a fuel economy rating of 40.8 km/l. The 2016 model year Prius has an official EPA fuel economy rating of 4.4 L/100 km for city, 4.7 L/100 km for highway, 4.5 L/100 km for combined driving. The new Eco version available in mid-grade level two trim, which features lithium-ion batteries, has an official EPA rating of 4.1 L/100 km city, 4.4 L/100 km highway, and 4.2 L/100 km combined. This improved efficiency is largely due to the reduced weight of the Eco, which has a lighter battery and does not carry a spare tire. As of March 2016, only three plug-in hybrid models available in the market have a higher combined fuel economy than the Prius Eco in terms of their combined EV mode/hybrid fuel economy, the BMW i3 (88 MPG-e), the Chevrolet Volt (77 MPG-e), and first generation Toyota Prius Plug-in Hybrid (56 MPG-e).