(1) All structures and obstructions, except as specifically mentioned in this section, eight feet (8′);

(2) All posts, pipes, crossing signals, and similar obstructions, eight feet (8′);

(3) Platforms eight inches (8″) or less above top of rail, four feet (4′) and eight inches (8″);

(4) Platforms four feet (4′) or less above top of rail, seven feet (7′) and six inches (6″), except platforms of railroad freight warehouse stations and freight transfer points, which shall have a clearance of not less than five feet (5′) and nine inches (9″);

(5) Platforms more than four feet (4′) above top of rail used principally for loading and unloading refrigerator cars, eight feet (8′);

(6) Switch boxes, switch operating mechanisms, and accessories necessary for the control and operation of signals and interlockers, projecting four inches (4″) or less above top of rail, three feet (3′);

(7) Low switch stands, dwarf signal stands and derail stands at center line of stand, six and one-half feet (6½′);

(8) All structural parts of railroad bridges shall have clearances which conform to the recommendation of the A.R.E.A. in effect when construction is begun;

(9) The side clearances specified in this section shall not apply to mail cranes during such times as the arms of such cranes are supporting mail sacks for delivery; provided, that the top arm is not lower than ten feet (10′) and eight inches (8″) above top of rail and neither arm extends within six feet (6′) and five inches (5″) from the center line of track;

(10) Icing platforms, seven feet (7′); and

(11) All minimum side clearances prescribed in this section are for tangent tracks. All structures adjacent to curve tracks shall have an additional minimum side clearance compensated for the curvature. Structures constructed prior to April 13, 1949, may be maintained at such clearance as was lawful at the time of construction.