Before any state highway, county road, or city street is closed to, or the maximum speed limit thereon reduced for, all vehicles or any class of vehicles, a notice thereof including the effective date shall be published in one issue of a newspaper of general circulation in the county or city or town in which such state highway, county road, or city street or any portion thereof to be closed is located; and a like notice shall be posted on or prior to the date of publication of such notice in a conspicuous place at each end of the state highway, county road, or city street or portion thereof to be closed or restricted: PROVIDED, That no such state highway, county road, or city street or portion thereof may be closed sooner than three days after the publication and the posting of the notice herein provided for: PROVIDED, HOWEVER, That in cases of emergency or conditions in which the maximum time the closure will be in effect is twelve hours or less the proper officers may, without publication or delay, close state highways, county roads, and city streets temporarily by posting notices at each end of the closed portion thereof and at all intersecting state highways if the closing be of a portion of a state highway, at all intersecting state highways and county roads if the closing be a portion of a county road, and at all intersecting city streets if the closing be of a city street. In all emergency cases or conditions in which the maximum time the closure will be in effect is twelve hours or less, as herein provided, the orders of the proper authorities shall be immediately effective.