I saw a proposal for an oval system, ie more like an elongated stadium. No left turns. If you are coming onto this system and want to turn left, you actually turn right and go to the end where you turn around.

Or if you want to leave by turning left, you first go to the end, turn around and then turn right on the way back.

There are more lane changes in this system, so that's a minus. But traffic lights might not be mandatory. It would be possible to have a continuous central barrier etc.