I'm from Finland where we have this kind of "relative fines". While I generally agree with the concept, it should better take into account the household's total income & wealth.
E.g. I could get a fine of 1/2 of my monthly net income for driving 140 km/h (87 mph) on highway, which would hit hard our household (three kids, low income spouse, no savings), although no real harm or risk was caused to anyone.