It is unlawful for any person to place any obstruction upon or cause to be obstructed in any manner any street, sidewalk or public way, or part thereof, so as to render the passage of persons, vehicles or other travel thereon difficult, inconvenient, dangerous, or impossible except as otherwise provided in this chapter; provided, that this section shall not apply to any employee of the city, county or state while such employee is immediately and actively engaged in the maintenance, improvement or construction of any street, sidewalk or public way. (Prior code § 3-1-34)