Vehicle Lightweighting - Worth the Weight?

Automotive Research Center

Safety and Fuel Economy

There are two types of automotive standards that are continually discussed: safety and fuel economy.  Auto manufacturers are working to make vehicles safer and more fuel efficient.  Seatbelts and air bags were created for safety.  Advanced powertrain technologies have helped to improve the fuel economy rating of passenger vehicles.  The trend of vehicle lightweighting has both positive and negative consequences for both safety and fuel economy.

Is passenger safety being sacrificed for the sake of fuel economy?

Over the last 20 years, there has been a steady decrease in the use of mild steel and iron casting in the manufacture of vehicles.  These materials have been replaced by high-strength steel, aluminum, plastics and other composites.  This is referred to as lightweighting.  The heavier the vehicle the harder it is to improve fuel economy.  However, the concerns with lightweight materials are increased costs and diminished safety for the passengers.  The question then becomes is passenger safety being sacrificed for the sake of fuel economy?  Dr. Charles Kahane of the National Highway Traffic Safety Administration (NHTSA) concluded in 1997 that lighter and smaller vehicles are less crashworthy than larger, heavier vehicles like SUVs.  But they do help automakers to comply with the stringent CAFE standards.

Vehicle lightweighting is not new

Vehicle lightweighting is not new.  Significant lightweighting, 30-40% in fact, was experienced between 1979 and 1985.  Auto manufacturers were facing tougher Corporate Average Fuel Economy (CAFE) standards.  Since 1986, vehicle mass has increased for almost all vehicle segments.  Ironically, two of the key reasons for this are the addition of safety features and emissions-compliance components.  In fact, the weight of light-duty vehicles has increased 68 pounds per vehicle for safety features and 40 pounds for emissions components since 1975.  Comfort and convenience features of course have had the most impact on overall mass, with an increase of 143 pounds per vehicle since 1975.  So now automakers are faced with the challenge of utilizing lighter-weight materials to counterbalance all of that added weight.

The advanced materials that are used in vehicles in place of steel have less mass.  Aside from safety concerns, there are other negative consequences as well.  Methods and tools used to repair lightweight materials is expected to become more diverse, making repair and replacement of such components after a crash for example more expensive.  A perfect example of this is front and rear bumpers of passenger vehicles.  If you are in an accident and one of the brackets on your bumper breaks or is damaged, many times it cannot be fixed or replaced.  Instead, the entire bumper requires replacement, resulting in higher costs to replace parts and therefore likely higher insurance premiums.

According to the Center for Automotive Research (CAR), we can expect to see the substitution of more aluminum, magnesium and composites become more widespread in the next ten to fifteen years.  This will have a significant impact on both the vehicle and the motorist.  While vehicles may handle and brake better, vibration is likely to increase.  And the debate will continue over whether or not lighter vehicles are as safe to the occupants.  For all of these reasons, the Auto Club will be keeping a close watch on vehicle lightweighting in the years to come.