The permittee shall protect with adequate and sufficient warning lights and devices any opening or obstruction placed in the street right of way. Warning lights and devices shall be placed in such manner as to be seen distinctly by all users of the street right of way at all times of the day and night. Whoever shall neglect to perform the duty imposed herein shall, in addition to the penalty provided by this chapter, be liable for all damages to persons or property caused by such neglect.