Which would be fair, because the goal of these things is to avoid misbehaviour with potentially deadly consequences. There is no reason someone poor should pay 40% of their monthly paycheck while someone rich pays with This is why in a lot of european nations on top of the fines you have a point-based system – if you have three points you get your driving license revoked and you will have it revoked for some time and then you have to do some driving tests again.
This actually works quite well in preventing bad behaviour (assuming you have a non corrupt police), but one could argue that it is a much, much worse punishment to the poor again (it can potentially destroy them economically, including the loss of income source etc).