On a multiple span bridge at night, how is the main navigable channel indicated?

The main navigable channel on a multiple span bridge at night is indicated by using three white lights in a vertical line. This configuration is standardized in navigation aids because it provides clear and easily distinguishable guidance for vessels approaching the bridge. The vertical alignment helps to ensure that mariners can identify the channel from a distance and understand that this is the direction they should take when navigating through the bridge.

The use of three white lights is especially effective at night since they can be easily seen against the dark backdrop, offering a definitive indication of the center of the navigable channel. It is essential for navigational safety, as it helps prevent collisions with the bridge structures and ensures smooth passage for vessels of various sizes.