Car is a necessity for people not living near public transportation. Such as rural areas, farmers, and many outlying suburbs. Car is a necessity for those folks. Which then means auto insurance is a mandate.
Auto insurance is only required for driving on public roads, and then, only the driver is mandated to buy the insurance. Only for the driver. Not everyone in the home needs auto insurance. That's NOT the case with the health insurance mandate.
And as has be pointed out earlier, the Constitution doesn't give the federal government the power to mandate individuals buy anything. If the SCOTUS decides otherwise, we'll know that the great experiment that was the republic is no more.
Mark