N.Y. Veh. & Traf. Law § 1652-B
The county superintendent of highways of Suffolk county may, when authorized by the Suffolk county governing board, erect and maintain traffic signs, signals and markings on, and provide traffic engineering services in relation to any highway, road or street within a town or village within such county, except state highways maintained by the state, providing the governing body of the town or village having jurisdiction over such highway, road or street determines on the basis of an engineering and traffic investigation that such traffic signs, signals and markings are necessary, issues any necessary ordinance, order, rule or regulation with respect thereto, consents to the erection and maintenance of such traffic signs, signals and markings by the county and consents thereto by written agreement with the Suffolk county governing board as to the extent of the authority and responsibility of the county superintendent of highways of Suffolk county and any apportionment of costs for the erection and maintenance of signs, signals and markings and traffic engineering services. The power granted to the Suffolk county superintendent of highways by this section shall in no way diminish any power over roads granted to him by law but shall be in addition to any such powers.
N.Y. Veh. and Traf. Law § 1652-B