The overpass of St. George Boulevard over I-15 reopened with a new configuration the other day, and I went through it for the first time last night.
It definitely freaked me out the first time. But it was totally painless. And I spent the next 20 minutes or so trying to visualize how it works, and why it might be a better idea.
My student TS had described it in class as a diverging diamond interchange.
Basically, all traffic crosses to the “wrong” side of the road as you go onto the bridge, and the crosses back to the “right” side of the road as you leave the bridge.
In modest traffic around 8:30 PM, the crossover went so smoothly that I was done before it registered on me. And then I was in a large, uncongested area, with an easy left turn onto I-15.
There was definitely a holy cow, how the heck did that magic trick work feeling to the whole thing.
They replaced something that worked like this: Note the intersections of arrows at the bottom right and top left. Those were handled with signals that had to cycle through 3 directions and 2 left-turn lanes.
The new interchange looks like this:
There are still two signals on either side of the bridge. But now they cycle through 2 directions instead of 3, and there are zero left turn lights.
Where I grew up this was all handled with cloverleaf interchanges. Of course, those are much larger. But further, you can’t retrofit an interchange for cloverleafs without using eminent domain to remove some of the properties built up around the interchange.