Deposits of excavated material or any other obstructions placed in the street right of way about the work site shall be placed in such manner as to insure the least inconvenience to users of the street right of way. The opening and all obstructions shall be protected with adequate barricades during the time work is not in progress. The Director of Public Service may require that all trenches or other unfilled openings be covered by a metal plate sufficient to maintain uninterrupted vehicular or pedestrian traffic and may further specify the type and number of barricades as may be necessary to reasonably protect the public against injury to any person or damage to any property.