“To the extent that the National Manual on Uniform Traffic Control Devices (hereinafter referred to in this section as MUTCD), promulgated by the Federal Highway Administration pursuant to subpart F of part 655 of Title 23 of the Code of Federal Regulations and subject to a public comment period under federal law, does not conflict with the provisions of this chapter and the provisions of other laws of the state, the National MUTCD shall constitute such state manual and specifications; provided, however, such manual and specifications may be modified by the commissioner of transportation by the adoption of a supplement or supplements as such commissioner of transportation determines warranted and in compliance with the applicable provisions of the state administrative procedure act. The National MUTCD and its specifications are adopted as the state standard for traffic control devices on any street, highway, or bicycle path ‘open to public travel’. No person shall install or maintain in any area of private property used by the public any sign, signal, marking or other device intended to regulate, warn or guide traffic unless it conforms with the state manual and specifications maintained under this section.”