I think you misunderstood my post. I was agreeing with you. That said, the study does not answer question 1. It answers who gets stopped by police. It does not answer the harder question of who is committing crimes. That's a much harder question to put numbers on because crimes are committed in private and most are not solved. You can use arrest or conviction rates as a proxy for that number; but there are a lot of confounding factors that make arrest and conviction rates by race not much more than a very rough cut at the number.
There are two studies, first the improper one this thread started off about and second, the The New Jersey Study linked to later on. The New Jersey study answered question 1. It was not based on arrests but on pictures of all drivers and their speed.
One way to look at that is to use victimization studies. A victimization survey gets data from victims who report the race of the offender, not the criminal justice system. These studies consistently confirm criminality rates observed in arrest and conviction studies.