The new Volkswagen XL1 Super Efficient Vehicle (SEV) has been  unveiled at the Qatar Motor Show. Pioneering construction techniques, an  advanced plug-in hybrid drivetrain and innovative packaging all play a  part in allowing the XL1 to return 260 mpg on the combined cycle to set a  new benchmark for vehicle efficiency.  Powering the XL1 is a compact  800 cc TDI two-cylinder common rail diesel