What Do The Stoplights At The Top Of Minnesota’s Iconic Lift Bridge Mean?

Whether you live in Duluth or you've just visited town, you've seen one of Minnesota's most iconic bridges. Besides being an important element of both car and ship traffic in Duluth, it is also a popular tourist destination.

Lots of locals and tourists alike spend time by the Lift Bridge throughout the year, enjoying beautiful views of Lake Superior and the Duluth hillside as well as watching ships come and go from Canal Park.

While thousands of people each year spend time by the Aerial Lift Bridge, only a small fraction of people know about the stoplights found at the top of the bridge. Sure, there are stoplights on either side of the bridge at ground level for controlling vehicle traffic, but the other stoplights at the top of the bridge are something far fewer people know about.

Where are the stoplights on the Duluth Aerial Lift Bridge?

If you look up at the top of the cityside tower (the northern upright structure) on the bridge, you'll see a pair of stoplights. One faces Lake Superior, while the other faces the Duluth Harbor.

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As you can see in the image above, these stoplights are hung horizontally, which is the opposite of normal automobile stoplights (which hang vertically).

What do the lights on top of the Duluth Aerial Lift Bridge mean?

While I've heard some people guess that the stoplights are an indicator for when it is safe for a ship to pass underneath the bridge, that's actually not what the lights are for.

The lights were installed as an indicator for water currents through the canal under the bridge. While the St. Louis River flows through the harbor and into Lake Superior through both the Duluth and Superior entry to between the harbor and the lake, the current isn't always in the same direction.

Depending on various factors, sometimes the current flows outward to the lake, while other times it flows inward into the harbor. The lights are an indicator not only of what direction the current is moving, but also what the current's speed is moving at.

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As the Duluth Yacht Club explains, a green light generally indicates an outward flow and red means there's an inward flow, but there's more to the code than just that. There are actually 5 total light configurations that can be used for those navigating the canal. Here's what each means:

• Flashing Green: Outbound current 3 mph or greater
• Steady Green: Outbound current more than 1 mph but less than 3 mph
• Yellow: "Neutral current", or a current less than 1 mph in either direction
• Steady Red: Inbound current more than 1 mph but less than 3 mph
• Flashing Red: Inbound current 3 mph or greater

The next time you get up close to the bridge, take a peek at the top of the cityside tower and look to see what the light is doing, and you'll know what the current is doing in the canal!