It's a single point urban interchange. Instead of having a traffic light on each side of the highway like a diamond interchange, it has only one at a single three way intersection. It winds up saving a phase on the lights, having a single three phase traffic signal instead of a pair of two phases.

The first phase is for through traffic on the street that's perpendicular to the freeway (if this road were extended out a little bit, it would be easier to visualize).

The second phase is for traffic exiting the free way from either direction and turning left. They'd exit the free way and take an immediate left toward the center. Those turning right don't need to use the light.

The third phase is for traffic entering the freeway with a left turn. Again, traffic turning right doesn't use the single point intersection.

It's to remove traffic that wants to swap to the other side of the highway without actually needting to go on it

I wonder... what's the point of the crossing ways under the highway?