[Noah930]

Good question: what's the difference between a set of double yellow lines for the carpool lane, and a double double set of yellow lines?

Well, on a regular street, there is a difference. For a set of double yellow lines, you aren't allowed to pass (go around into oncoming traffic)a slower vehicle in front of you. With a set of double double yellow lines, not only are you not allowed to do that, but you can't even make a left turn into a driveway. With a single set of double yellow lines, you can't pass (by going into oncoming traffic), but at least you can make a left turn into a driveway.

So, extrapolating that to the diamond lane, I suppose that if you've got a single set of double yellow lines, you can't go around a slower car in front, but perhaps you're technically allowed to scoot into "regular" traffic to make an exit ramp? (But what about those designated white lined areas for entering/exiting the carpool lane?) But if there are a set of double double yellow lines, you can't do either maneuver?