(a) Passengers having an immediately prior or subsequent movement by air. The transportation of passengers by motor vehicle is transportation incidental to transportation by aircraft provided (1) that it is confined to the transportation of passengers who have had or will have an immediately prior or immediately subsequent movement by air and (2) that the zone within which motor transportation is incidental to transportation by aircraft, except as it may be individually determined as provided in paragraph (c) of this section, shall not exceed in size the area encompassed by a 25-mile radius of the boundary of the airport at which the passengers arrive or depart and by the boundaries of the commercial zones (as defined by the Secretary) of any municipalities any part of whose commercial zones falls within the 25-mile radius of the pertinent airport.

(b) Substituted motor-for-air transportation due to emergency conditions. Transportation of passengers by motor vehicle is transportation incidental to transportation by aircraft if it constitutes substituted motor-for-air service performed at the expense of the air carrier in emergency situations arising from the inability of the air carrier to perform air transportation due to adverse weather conditions, equipment failure, or other causes beyond the control of the air carrier.

(c) Individual determination of exempt zones. Upon its own motion or upon petition filed by any interested person, the Secretary may in an appropriate proceeding, determine whether the area within which the transportation by motor vehicle of passengers having an immediately prior or subsequent movement by air must be performed, in order to come within the provisions of paragraph (a) of this section, should be individually determined with respect to any particular airport or city served by an airport, and whether there should be established therefor appropriate boundaries differing in extent from this defined in paragraph (a)(2) of this section.

(d) Exempt zones and operations—(1) Dulles and Baltimore-Washington International Airports. The transportation by motor vehicle, in interstate or foreign commerce, of passengers, having an immediately prior or subsequent movement by air, between Dulles International Airport, near Chantilly, Va., and Baltimore-Washington International Airport, near Baltimore, Md., is partially exempt from regulation under 49 U.S.C. 13506(a)(8)(A).

(2) Savannah, Ga., Airport. The transportation by motor vehicle, in interstate or foreign commerce, of passengers, having an immediately prior or subsequent movement by air, between Savannah, Ga., Airport and all points on Hilton Head Island, SC, is partially exempt from regulation under 49 U.S.C. 13506(a)(8)(A).

(3) Chicago O'Hare International Airport (Chicago, Ill.). The transportation by motor vehicle, in interstate or foreign commerce, of passengers, having an immediately prior or subsequent movement by air, between O'Hare International Airport, at Chicago, Ill., on the one hand, and, on the other, points in Indiana on and north of U.S. Highway 30 and on and west of Indiana Highway 49, is partially exempt from regulation under 49 U.S.C. 13506(a)(8)(A).