There is lots of discussion about increasing the fuel standards from the present 27.5 of cars and 22.2 for trucks up to 35 mpg for all vehicles by 2020. This legislation is working its way through the U.S. Senate, and might become law. This represents a 40 percent increase in fuel economy standards from the present day. Quite a big change!
In order to achieve this sort of efficiency gains, drastic things must change in regards to the design of the automobile. There are some things that can be accomplished in drive-train design to improve economy, but much of the economy improvement will need to come from mass reduction. Vehicles will need a diet.
Anywhere and everywhere weight can be trimmed, it must. This largely means that steel and cast iron must be removed and replaced with other stronger, yet lighter materials. There are some metals such as titanium that will handle some applications. Aerospace-grade composites can handle others, both decorative and non-decorative. All of the exterior body panels will be made from composites. This technology is in some current production vehicles.
Structural composites do not have extensive current application in automobiles. I am sure they will be considered as this problem is faced. Lots of resin and carbon fiber will need to be used in vehicles where impact strength, bending strength, fatigue resistance, UV exposure, and abrasion resistance will be paramount. It will definitely be a tall order.
The amount of composites in future vehicles is very likely to increase in order to meet new fuel economy standards. New processes and engineering design will be necessary. All of these composites resins and reinforcements are expensive as raw materials and the processing will likely be expensive as well. Making composites competitive in this application will be the big achievement!