With the approval of the governor and council the commissioner may use the funds accruing to the department for construction and reconstruction and maintenance of class I highways and bridges thereon, for aid in construction and reconstruction of class II highways and bridges thereon, for maintenance and reconstruction of class III highways, for aid in construction, reconstruction and maintenance of class IV and V highways and aid in the construction of bridges thereon, for the providing and maintenance of buildings, equipment and supplies, for highway purposes, for the costs of administration, and for such other purposes as may be provided by law. The commissioner may designate all or any part of class I, class II or class III highways for winter maintenance.