The commissioner may close, regulate or restrict traffic over any section of any class I, class II or class III highway or bridge thereon when the public welfare or necessity so requires, or in order to perform work on any such highway or bridge by posting notices at each end of such section of highway or at each end of such bridge, and may establish and mark detours, and no town shall be liable to any person for damages or injuries caused in whole or in part by the use of such highway or bridge when such notices are posted. Any person who travels on a closed highway or bridge or who violates the provisions of such regulations or restrictions shall be fined not more than $100.