How does the use of aluminum result in higher gas mileage and reduced vehicle emissions?

Aluminum is used in vehicles by substituting aluminum parts in place of heavier iron/steel parts (e.g., vehicle hoods, trunk lids, door panels, radiators, heat exchangers, drivetrain castings, etc.). According to the Aluminum Association, a 6% to 8% fuel savings can be realized for every 10% reduction in vehicle weight achieved by substituting aluminum parts for heavier steel parts. Lower fuel consumption, in turn, results in lower emissions.