In the last photo you can see that the traffic cones are translucent.

I think it's the regulation rollover protection. If you draw a line from the top to the front wheels it clears the driver's head. Though if you rolled in dirt I don't think it will help you.

I also think this is why the new closed cockpit prototypes look so silly. I prefer the coned sticking out.

Thanks John for directing us toward that great documentary. I have downloaded it and washed it perhaps 10 times. As for the nipple-shapped cones, I can't see what their purpose is. Maybe there's a thick tube inside each of the cones.