From what I get from skimming the paper he suggests that America's focus on cars might be related to the end of segregation, with cars allowing white people to just decide to live in a neighborhood with few black people. Effectively the policy shift towards cars enabled a new form of segregation.

Additionally "Experiments have found that motorists yield less often for people of color." (page 27).

But those are minor tangents in a 100 page rant about laws and enforcement (as well as victim blaming in traffic accidents)