Most countries in western europe have a concept of day-fines. It's averaged income minus essential expenses multiplied by some amount of time.

Fictional example: speeding 20km/h above the limit gets 30 day-fines. So they'll calculate how much you'd earn in 30 days, subtract essentials and that's your fine.

This could be a problem in the US because of how "income" is measured and reported by the rich (among many reasons).

It would still help the poorest. Figuring out how to define income for the upper end could be done separately.