Set to arrive by 2015, the fourth-generation Toyota Prius is expected to be a evolution of the current model and will feature a slicker design as well as lighter materials. Moreover, the vehicle will feature tires with lower rolling resistance in order to improve its fuel efficiency. The current model came on the market back in 2009 and is rated by EPA at 51 mph in city driving and 48 mpg on the highway. The new generation is expected to improve these numbers and according to Inside Line the Japanese manufacturer believes that the rolling resistance is a key element in improving the fuel efficiency. As a result, it is already collaborating with tire manufacturers in order to achieve these improvements. Regarding the lighter materials, it appears that Toyota considered making the body of the second-generation Prius from aluminum but due to the fact that this material asks for high investments it abandoned the idea. Still the Prius V and Prius+ have an aluminum hood.