Every person temporarily occupying any public street or sidewalk, as in this Chapter provided, shall safeguard the public interest by erecting barriers at or near either approach of said obstruction, and shall during the period from one hour after sunset to one hour before sunrise, display thereon a red light, visible at least two hundred feet (200') in the direction in which the travel is proceeding; provided, that any vehicle left standing in the street during the nighttime shall be safeguarded by lights as in this Section provided; and, provided further, that no vehicle shall be left standing in alleys during the nighttime, in a manner that will obstruct traffic.