by Zach McDonald | HybridCars.com The Toyota Prius family was the best-selling vehicle line in California over the first half of 2013, moving more than 170,000 total units through June of this year. But despite progressively growing sales numbers each year in California and around the country—as well as the release of three new Prius models including the Prius c, Prius v and Prius Plug-in—Toyota hasn’t actually given the platform a true overhaul in more than four years. toyota-prius-hybrid In 2009, improvements to Toyota’s Hybrid Synergy Drive system and the vehicle’s overall design netted an increase in the Prius’s average fuel economy rating to 50 mpg. Since then, no other carmaker has managed to match that number in a pure hybrid. Recently though, at an event in Ypsilanti, Michigan, Toyota Managing Officer Satoshi Ogiso gave journalists a sneak peak at what’s in store for the new generation of Prius family vehicles. First and foremost on the list of improvements will of course be fuel economy—the driving factor in the Prius’s success over the last decade. According to Ogiso, the next Prius will feature a 10 percent improvement in fuel economy, pulling average efficiency up to 55 mpg. The increase will come as a result of a redesigned Hybrid Synergy Drive, lighter materials and a new battery pack, which is rumored to potentially be powered by lithium ion rather than nickel metal hydride. Handing will also improve, as Toyota works to lower the center of gravity of its cars under its New Global Architecture. Toyota also announced changes to the next generation Prius Plug-in, promising more electric range and possibly a wireless charging feature that the carmaker is currently testing. The fourth generation of Prius is scheduled to hit the road sometime in 2015.