117.389—Calumet River.
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.