Introduction
A Diverging Diamond Interchange (DDI) is a modern interchange design that temporarily shifts traffic to the opposite side of the road when crossing a freeway. This unique setup makes left turns onto and off the freeway faster and safer by eliminating the need to cross opposing traffic.
How a DDI Works
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Crossover Lanes – As you approach the interchange, traffic crosses over to the left side of the road at a signal-controlled crossover.
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Free Left Turns – Because you’re already on the left side, you can turn directly onto the freeway without waiting for a separate left-turn signal.
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Crossover Back – After passing the freeway, traffic shifts back to the right side of the road.
Steps for Driving Through a DDI
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Approach Carefully – Watch for overhead signs and lane markings showing the crossover pattern.
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Follow the Signals – Traffic lights at the crossover points guide you to the correct side of the road.
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Turning Left onto Freeway – Simply follow the left-turn lane and merge directly without crossing oncoming traffic.
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Going Straight – Continue through the crossover and back to the right side after the interchange.
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Exiting the Freeway – Left turns from the ramps blend easily into the traffic crossover.
Benefits of a DDI
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Increased Safety: Fewer conflict points mean fewer chances of crashes.
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Improved Flow: Reduces congestion during rush hours.
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Efficient Left Turns: Eliminates long waits for left-turn arrows.
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Pedestrian Safety: Crosswalks are shorter and more visible.
Common Mistakes to Avoid
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Hesitating at the crossover because it feels unusual to drive briefly on the left side.
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Missing lane signs and trying to change lanes at the last second.
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Not paying attention to signals and lane markings.
Where You’ll See DDIs in Utah
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I-15 at American Fork (Main Street)
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I-15 at Layton Parkway
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I-15 at St. George Boulevard
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And more locations under development by UDOT.
Why It Matters
DDIs may look confusing at first, but they are designed to reduce congestion and improve safety on Utah’s busy highways. With practice, they become easy to navigate, offering smoother travel for drivers.
✅ Takeaway: A Diverging Diamond Interchange shifts traffic to the left side of the road at the interchange, allowing for safer and quicker left turns onto and off the freeway. Always follow the signals, lane markings, and signs carefully.