In my younger days, I experienced more than a couple traffic stops. Reasons ranged from driving allegedly unsafe vehicles, speeding, tinted windows, and even in one bizarre interaction, not having a tailgate on my truck. The traffic stops themselves ranged from somewhat confrontational to quite pleasant. However, I am white and am well aware that this fact probably played a role in the outcome of some of these situations. The Stanford "100 million stops" study showed that nationally, minority drivers are not only more likely to get pulled over in the first place, they are more likely to be subject to searches and more likely to get a ticket. A recent Motherboard story even suggested that maybe that was the goal of officer discretion in the first place.
There is also a rather well-documented trend of municipalities becoming increasingly dependent on traffic fines and court fees as sources of revenue. It is eerily similar to the “policing for profit” concept involving civil asset forfeiture I wrote about in 2017. Over on the west coast, the city of Berkeley, California, is actually looking at taking traffic stops completely away from police and handing those duties over to the Department of Transportation. It will be interesting to see whether their experiment has ripple effects around the country.