Local authorities in their respective jurisdiction shall place and maintain such traffic-control devices, conforming to the state manual and specifications, as they may deem necessary to indicate and carry out the provisions of this chapter or local traffic ordinances, orders, rules or regulations or to regulate, warn, or guide traffic, except that a city having a population in excess of one million shall conform to the state manual and specifications only insofar as such local authority in its discretion deems practicable.
New York Legal Code