What is the easiest way to prohibit a "u-turn" at an intersection on a divided road?
This is the location in question:https://www.waze.com/cartouche_old/?zoo ... FFFFFFTTTT
In this example, I could just block the turns on the small connecting road section. But if there were parking lot roads (or actual side streets) at that intersection, that would potentially block the allowed turns.
There's a few solutions:
The easiest is to create a Mapcat Bowtie, collapse everything to a single junction, disable all turns on the junction, then manually enable each allowed turn and fix up the geometry to look reasonably ok.
A second solution is to use dedicated turn lanes in combination with appropriate turn restrictions to prevent the u-turn, this works well with large medians and wide streets with actual dedicated turn lanes. For a full on dual-carriage to dual-carriage intersection you end up with a Crossed Box. This actually looks reasonably good on the client as there's no pinch as with the Bowtie and the intersection is just one blob.
A third solution, probably most error prone and confusing, is to used stacked two-way roads with appropriate turn restrictions. You have to temporarily modify their geometry enough to set turn restrictions correctly, but it does work.