(a) An existing object, including a mobile object, is, and a future
object would be, an obstruction to air navigation if it is of greater
height than any of the following heights or surfaces:
(1) A height of 500 feet above ground level at the site of the object.
(2) A height that is 200 feet above ground level or above the
established airport elevation, whichever is higher, within 3 nautical
miles of the established reference point of an airport, excluding
heliports, with its longest runway more than 3,200 feet in actual length,
and that height increases in the proportion of 100 feet for each
additional nautical mile of distance from the airport up to a maximum of
500 feet.
(3) A height within a terminal obstacle clearance area, including an
initial approach segment, a departure area, and a circling approach area,
which would result in the vertical distance between any point on the
object and an established minimum instrument flight altitude within that
area or segment to be less than the required obstacle clearance.
(4) A height within an en route obstacle clearance area, including turn
and termination areas, of a Federal airway or approved off-airway route,
that would increase the minimum obstacle clearance altitude.
(5) The surface of a takeoff and landing area of an airport or any
imaginary surface established under §77.25, §77.28, or §77.29. However, no
part of the take-off or landing area itself will be considered an
obstruction.
(b) Except for traverse ways on or near an airport with an operative
ground traffic control service, furnished by an air traffic control tower
or by the airport management and coordinated with the air traffic control
service, the standards of paragraph (a) of this section apply to traverse
ways used or to be used for the passage of mobile objects only after the
heights of these traverse ways are increased by:
(1) Seventeen feet for an Interstate Highway that is part of the
National System of Military and Interstate Highways where overcrossings
are designed for a minimum of 17 feet vertical distance.
(2) Fifteen feet for any other public roadway.
(3) Ten feet or the height of the highest mobile object that would
normally traverse the road, whichever is greater, for a private road.
(4) Twenty-three feet for a railroad, and,
(5) For a waterway or any other traverse way not previously mentioned,
an amount equal to the height of the highest mobile object that would
normally traverse it.