Most Roadgeeks know what a Diverging Diamond Interchange is, but for those who don't:
What it does is force drivers crossing over a freeway to briefly crossover to the wrong side of the road. This allows left turns to be made without crossing the opposing traffic. They've been spreading like wildfire in the last 15 years due to the safety and traffic flow benefits they offer.
But there have been ideas for improving on the DDI.
A relatively simple one is to add left turn loops and make it a Diverging Partial Cloverleaf. The benefit of this is it eliminates the weaving of left turns.
Another idea is to get rid of the crossover for drivers going straight but keep for those who are turning left. The
designer describes it as a Splintered Untwisted DDI. This gets rid of a current problem with DDIs in that they can't allow traffic go straight in both directions at the same time. But it does require a wide (read: expensive) bridge structure
And another idea is to grade separate the crossovers. The
patent holder describes it as a "Double Crossover Merging Interchange". This makes the DDI into a free-flow interchange and thanks to the way that left turns off the freeway rejoin the mainlines, it eliminates weaving. But of course, flyovers are very expensive. Also, if you take two of these, you get a diverging windmill interchange.
These are all very interesting designs and I hope we see them on the road some day.