Highways are absolutely a profit center. The Fed spends ~$50 billion/year on highways and gets ~20% of the entire productivity of the nation in return. ($4 trillion on $20 trillion GDP)
If the entire highway system increases GDP at least $250 billion (1.25% of GDP) then highways are profitable.
But the government didn’t build them for free. We collectively paid to build them, and now they more than pay for themselves. Roads are arguably the greatest investment the American taxpayer has ever made.
Building pubic-use roads without government planning, permitting, and eminent domain is frankly not going to scale, aside from the nightmare of how all the different owners of these roads would go about rent-seeking.
If the entire highway system increases GDP at least $250 billion (1.25% of GDP) then highways are profitable.