The draws of the Norfolk Southern railroad bridges, miles 1.32 and 1.36 at Chicago, operate as follows:

(a) The draws shall open on signal; except that, if either one of the bridges is inoperable because of equipment breakdown, the other bridge need not be opened.

(b) In addition to the signals prescribed in § 117.15, the following special visual signals shall be used on the bridges:

(1) When the draw cannot be opened immediately, or is open and must be closed promptly, two red lights are flashed alternately.

(2) When the draw can be opened immediately, two amber lights are flashed alternately.

(3) When the draw is open for passage, two green lights are flashed alternately.