Well, yeah, billboards can definitely be racist.
https://goo.gl/maps/tqqyuc7Z2WLdWY1t7
Didn't even have to click the link to know where it was going to take me.. I expected nothing less from Harrison.
From what I've heard, a lot of them used to be scattered all over North Carolina. Supposedly, one was even along I-95 in Fayetteville, but I don't remember seeing it.
As for the original question, no matter how much racism exists in the country, you can't convince me that any municipality has ever built roads just to throw black or Hispanic people out of their homes. I don't care if it's in Baltimore, DC, Chicago, Atlantia, Miami, the Bronx, Brooklyn, Boston, Syracuse, or anywhere else. Maybe some racists could see it as an additional benefit, but that's it.
Here's a reminder; Robert Moses built highways through poor and rich neighborhoods alike.