This doesn’t speak exclusively to blacks, but during the Ferguson flap, it was reported that the reason so many blacks were with more warrants that resulted in more arrests, were over past tickets. They could not afford to pay the fines (which supported City Hall) as easily as the whites would pay their tickets. More blacks were out of work and the City used the ticketing racket to run the budget. Blacks paid the higher price in the increased arrest statistics, over basically traffic stops.
Whether that is even true or not, I dunno. If it is, it makes sense.
I took a brief look at Ferguson’s city income from fines and court fees versus that of some other suburban cities in a major metro area. Their income on a by population basis seemed out of whack to me.
This is a subject that probably deserves a better look than it gets. It would require a numerate investigative journalist, which is almost like wishing for a unicorn.