A related--albeit more "out-there"--idea is to impose momentum limits in addition to speed limits based on vehicle weight classes. We have a crude version of this on highways, where speed limits for trucks are often lower than the limits for cars (e.g., 70mph for cars, 65mph for trucks).
But I really like the idea of setting different speed limits for different weight classes of vehicles. Driving a Toyota Corolla? Let's call it a Class A vehicle (2,000-2,999 lbs), with a highway speed limit of 70mph. Driving a Jeep Grand Cherokee? That would be Class C (4,000-4,999 lbs), with a speed limit of 50mph.
This would make roads a lot safer, and add an additional, non-monetary, tax on heavier vehicles.
Another big benefit of imposing weight limits on consumer vehicles is that the United States would have a fighting chance of becoming energy independent, even before accounting for the shift to renewables. So we can add improved national security to the list of reasons to pursue this common-sense policy.