How will greenhouse gases (GHG) and carbon dioxide (CO2) emissions from cars and trucks be regulate?

Question

With increasing global concern over climate change and global warming, state officials have begun enacting regulations designed to reduce vehicle emissions pollution. The federal government is slowly recognizing that its regulatory role is being usurped by the states and may begin to regulate vehicle emissions through the Environmental Protection Agency’s enforcement of the federal Clean Air Act.

***This is something i am learning educationally. Don't worry will not plagiarize, this is part of my research and so i can better understand my subject. Thak you.***

Answer 1

for cars?  easy.  better mpg.  double the miles per gallon, and cut the CO2 in half.

trucks have it harder.