The day-fine system is kinda interesting, because it recognizes that the impact of paying a $500 fine is very different based on your income.
I was surprised to learn that the UK experimented with it, briefly, but it's something that exists in several other countries for example Finland has had the system since 1921.
For speeding, we do have a fine based on your weekly income. It can be up to 175% of your weekly income (capped to £2,500), if doing >100 MPH on a motorway (or >76 MPH if speed restricted to 50 MPH).
I was surprised to learn that the UK experimented with it, briefly, but it's something that exists in several other countries for example Finland has had the system since 1921.
https://en.wikipedia.org/wiki/Day-fine