Veh. Code, § 21102

Local authorities may 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 in the opinion of the legislative body having jurisdiction such closing is necessary for the protection of persons attending such school or school grounds. The closing to vehicular traffic may be limited to such hours and days as the legislative body may specify. No such ordinance or resolution shall be effective until appropriate signs giving notice thereof are posted along the street or highway affected, nor in the case of state highways, until such ordinance or resolution is approved by the Department of Transportation.