The superstructure of a bridge should be lighted in accordance with the following specifications.

(1) Where the bridge structure is over navigable water, approval of the lighting installation must be obtained from the commandant of the United States Coast Guard to avoid interference with marine navigation.

(2) Specification "F-1." When the bridge superstructure is not more than 150 feet in over-all length.

(a) There should be installed at the approximate center of the highest point of the superstructure at least two lights, each light consisting of a lamp of at least 100 watts, enclosed in aviation red obstruction light globes. The two lights should burn simultaneously and should be positioned so as to insure unobstructed visibility of at least one of the lights from aircraft at any normal angle of approach.

(3) Specification "F-2." When the bridge superstructure is more than 150 feet in over-all length.

(a) There should be installed for each 150 feet, or fraction thereof, of the over-all length of the bridge superstructure one or more lights, each light consisting of a lamp of at least 100 watts, enclosed in aviation red obstruction light globes. These lights should be installed on the highest points of the superstructure at approximately equal intervals not exceeding 150 feet in a manner to indicate the general definition and extent of the obstruction, and to insure unobstructed visibility of the lights from aircraft at any normal angle of approach. The distance between these top lights may be increased to a distance not exceeding 600 feet when the particular bridge is located more than 15,000 feet from the reference point of any landing area.

(b) Where the bridge superstructure exceeds 150 feet in over-all length and the use of the above described obstruction lights would be impracticable or inadequate, flashing or rotating hazard beacons should be used as an alternate to the fixed obstruction lights. Such beacons should be located on the highest points or edge of the bridge superstructure at intervals not exceeding 3,000 feet, provided at least three beacons are installed to indicate the extent of the obstruction. The flashing or rotating beacons should conform to the provisions of the pertinent specifications as hereinbefore indicated under "obstruction lighting equipment."