(a) A municipality is relieved of any and all liability resulting from or occasioned by defects in the public roads of its municipal street system when it has not been negligent in constructing or maintaining the same or when it has no actual notice thereof or when such defect has not existed for a sufficient length of time for notice thereof to be inferred.

(b) A municipality is relieved of any and all liability resulting from or occasioned by defective construction of those portions of the state highway system or county road system lying within its corporate limits or resulting from the failure of the department or the county to maintain such roads as required by law unless the municipality constructed or agreed to perform the necessary maintenance of such road.