Existing law authorizes local authorities to adopt rules and regulations by ordinance or resolution closing to vehicular traffic that portion of any street or highway crossing or dividing any school ground or grounds when necessary for the protection of persons attending the school or school grounds. Under existing law, an ordinance or resolution pursuant to this authority is not effective until after appropriate notice signs are posted along the street or highway affected, or, in the case of state highways, after the ordinance or resolution is approved by the Department of Transportation, as specified.