by Zach McDonald | HybridCars.com Over the last dozen years, Volkswagen has gradually been working to perfect a concept car so revolutionary in its fuel efficiency that it was known as the “One-Liter.” The naming reflected VW’s original goal for the car, to produce a vehicle that could travel 100 kilometers on a single gallon of fuel. vw-xl1-wolfsburg Now, with the addition of a small lithium ion battery pack and plug-in hybrid charging capability, the One-Liter has evolved into the XL1, a limited-run production vehicle that will not only meet, but exceed the original goal of 100 km/L fuel economy by 10 km/L. VW recently invited a small group of journalists to drive the car in Wolfsburg, Germany, giving them a chance to peep some of the more nuanced fuel-saving features and find out how the final production vehicles drive. The verdict form PluginCars.com is that while the XL1 most certainly wasn’t built to appeal to the mainstream, its single-minded focus on reducing inefficiencies provides a unique look into the future of automotive transportation. The most noticeably deviant feature of the XL1 compared to other cars is its shape. With a wider front that tapers off into a teardrop-like rear, the XL1 was designed to be among the most aerodynamic vehicles ever on the road. A coefficient of drag of just 0.19 blows production plug-ins like the Nissan LEAF and Chevy Volt (which both have a 0.28 coefficient,) and the Tesla Model S (0.24) out of the water. Another measure Volkswagen undertook to reduce drag was the elimination of side and rearview mirrors in favor of cameras that display on screens inside of the cockpit. This approach saves weight and drag on the vehicle, and is an example of a feature that may see its way onto production vehicles from a number of carmakers in the future. Full-sized power windows have also been replaced by small, hand-cranked miniature sub-windows which exist as part of the full window glass on the driver and passenger-side doors. This kind of feature, as well as minimal sound-proofing that makes every bump and acceleration audible to those inside of the cabin, is likely a sacrifice that would be unacceptable to mass-market consumers. For Volkswagen though, the XL1 is still largely a test vehicle, even if 250 will soon be made available on the European market. What the company learns from its experience with the XL1 though will likely pave the way for a number of future fuel-saving innovations available to the greater market.