For a scrappage program, I think the best model would be something that's broad-based to try to get at the 35% of vehicles 12 years old and older. If you look at total fleet emissions, it's those older vehicles that are going to be polluting more and putting out more GHGs than new vehicles. While ZEV adoption is critically important, you need to turn over the vehicle fleet at a faster pace. It currently takes about 20 years to fully turn over the fleet.
A scrappage program should aim at vehicles 12 years old and older and it should give consumers an incentive not just to purchase a ZEV vehicle, but also to purchase a new, efficient ICE vehicle. If you do that, you're still going to see a huge gain in terms of emissions.