As far as I know, the problem here is police running photos that it has from some cameras against the DMV database. Which is a) apparently of dubious legality because it's a biometric search and should be done in a criminal case but is instead done promiscuously left and right; and b) is ethically dubious because it creeps into the territory of ubiquitous surveillance.
Vehicles and roads don't enter the equation apart from people having gotten driver licenses. The licenses just make the largest database of US citizens' faces.
> [...] of dubious legality because it's a biometric search and should be done in a criminal case [...]
That is not the law. You have been misled, perhaps as the article's author intended. The author's feelings on whether such searches should be legal are not the same as democratically-enacted laws on the matter.
Vehicles and roads don't enter the equation apart from people having gotten driver licenses. The licenses just make the largest database of US citizens' faces.