Unless otherwise directed by a member of the Police Department or other authorized person, vehicles in or upon any grade separation shall at all times stay to the right of the center of all grade separations; slow moving vehicles shall remain as close as possible to the right hand side or curb of the grade separation; and where a grade separation is marked with traffic lanes, vehicles shall cross the markings only when overtaking and passing other vehicles. It is unlawful for the operator of any vehicle to cross any such marking unless such movement can be made with safety. (Ord. 3262-NS § 7.3, 1952)