Its not fuel economy laws, its the highway safety laws. Light cars are usually more efficient.
Maybe you're thinking of the strict emission laws regarding NOx and SOx that prevent diesel cars.
Maybe you're thinking of the strict emission laws regarding NOx and SOx that prevent diesel cars.
That's true, but US fuel economy standards don't actually require vehicles to be more fuel efficient in a direct way. They require vehicles to be a certain fuel efficiency for their footprint.
Unintuitively, while making a car larger doesn't make it more fuel efficient, it might make it better meet US fuel economy standards.