Section 28-642 - Traffic control signs on state highways; rulesA. The director shall place and maintain traffic control devices that conform to the manual and specifications prescribed in section 28-641 on all state highways as the director deems necessary to indicate and to carry out this chapter or to regulate, warn or guide traffic.B. A local authority shall not place or maintain a traffic control device on a highway under the jurisdiction of the director except by the director's permission.C. In cooperation with local authorities, the director shall synchronize traffic control signals on a state highway that has a traffic flow exceeding fifteen thousand motor vehicles per day in a vehicle emissions control area as defined in section 49-541.D. The director shall adopt rules pursuant to title 41, chapter 6 to establish criteria for the installation and maintenance of directional signs for universities prescribed in section 15-1601, for community colleges as defined in section 15-1401 and for the campus of a regionally accredited college or university.