I don't understand your argument. I don't know how gridlock on the highway system causes employment. I was born, raised, and currently reside pretty deep in the city of Chicago, so I'm familiar with commutes, though usually on public transportation, because the interstates are largely for long distance travel. They remain 2-3 hours a day (sometimes) without touching a highway, as they were before cars were even owned by average working class people. I have never owned a car in my life, and have no interest in or ability to drive.

The highway system is a result of government planning. If it hadn't been "held back" by government planning, it would lack existence. This would be a tax on every good imported into the city (which is virtually every good.)

I don't assume that highways are one aspect of central planning that works, I think that highways are one of a multitude of aspects of government (which I suppose you mean by "central planning") that are justified because, while not being profitable in themselves, they reduce friction for the entire system. The government is the only actor who can levy fees for that from the entire system, therefore the only one who can execute it.

If the tax base is eroded in a city, this is a failure of paperwork, not a physical event. If black people and the white people who ran from them were in slightly closer physical proximity, but still entirely homogenously clumped together (assuming a huge decline in public transportation not caused by the highways) you're saying that there would be some benefit to the urban poor?