An article in the Detroit News shows that there is some "softness" to these targets. For instance,
"Automakers can make improvements to air conditioning systems to reduce emissions without improving mileage. As a result, the standard will actually result in a fleet-wide average of 48.7 to 49.7 mpg by 2025."And then reality will rear its ugly head too:
"Taking into account real-world driving, the actual average will be around 40 miles per gallon in 2025."
Regardless of the exact final numbers, these improvements will only come about as a result of replacing more and more metal components with plastic components. That is not the only way to acheive these numbers, as better engine designs with and without the use of hybrid drives and all-electric vehicles will also play a significant role in future cars. But there still will always be neverending siren call to reduce vehicle weight further and further, and that means plastics will play an ever increasing role in the cars of the future. It's rather ironic that petroleum-based materials will play a key role in reducing the use of petroleum, isn't it.