> If you're rich and you get fined doing well over the specified speed limit but you only have to pay at most a few hundred dollars for potentially putting someone else's life in danger, what is the deterrent?

Many US states have a system of "points," which are assigned based on the severity of the driving offense. You might hear someone say "He got three points on his license for speeding."

The points expire over time, and points can be subtracted by attending driving school (and possibly other ways, too), but there are some limits on how quickly and how many points can be expired. Accumulating too many points at one time (the limit is usually an integer in the range 5 to 10) will lead to having one's license and driving privileges revoked.

The number of points earned for drunk driving is somewhere close to the maximum (in my state), and there are more restrictions on retiring these points, so being caught driving drunk puts one perilously close to losing one's license.

I'm not sure that either income-proportionate fines or license points are better. Just different approaches to the same problem.

Edit: Actually, after thinking about this a little more, I feel that the proportionate fines are probably better. Not all states have points systems, and points generally do not transfer between states. So someone from another state could come here, be caught speeding, and not face any long-term consequence (because the points would expire before they return).