Carrier routes usually aren't that well defined such that you have a white or a black neighborhood.
Oh... I think the amount of white only neighborhoods is a myth amongst the general public, and actually limited to communities of liberals, Democrats, and the ruling elite.
What identifies a neighborhood is the culture of crime that it either allows or doesn't.
Unfortunately, there is a large culture of crime rampant in the US. Starting with the President and going down to street thugs of all races and various nations.
For instance, there are 'gated' MUSLIM communities in the US, where I would not want to deliver the mail. Not that they would even let an American in, especially YOUR postman.
Apartment buildings are “GATED” ~ and some have supplemental fencing to separate street thugs from the residents.