Is there a street-legal modification we could make to small sedans that would massively increase the risk of death to an SUV/truck owner (and ideally only that) in the event of a collision? Until the lethal calculus is equalized, the arms race is going to continue. SUV drivers have to start dying.

I know it sounds extreme, but the fact that they don't die and that the other guy dies instead, is the entire reason they choose the SUV, even if they don't say it.

Until that changes, the best-response function is just going to keep returning "bigger SUV".

This is literally a matter of life and death, so fucking play to win. You need something like MAD, but specifically targeted at SUVs.