The state road commissioner shall exercise the same control over connecting parts of the state road system in municipalities, except the regulation of traffic, that he exercises over such system generally, but he shall assume no greater duty or obligation in the construction, reconstruction and maintenance of streets which are part of the state road system than he is required to assume in the case of state roads outside of municipalities. In order, however, to promote the safe and efficient utilization of such streets, the location, form and character of informational, regulatory and warning signs, curb and pavement or other markings, and traffic signals installed or placed by any municipality on any highway or street hereafter constructed with state or federal aid shall be subject to the approval of the state road commissioner.