These mandates currently require an average of at least 27.5 mpg for passenger cars and 21.5 mpg for light trucks. These mileage regulations conflict with other government regulated mandates for safety features such as airbags, side-impact collision beams, and antilock braking systems. Consumer demands for features such as power windows and door locks also reduce fuel efficiency. All of these extra features add significant weight which is detrimental to fuel efficiency. To accommodate these conflicting demands, automobile manufacturers have been looking for lighter materials to use in place of steel.
Aluminum alloys appear to be the most promising of the lighter materials available.