SAAB 9-X BioHybrid active rear aero - 10% improvement
 

Of course you ask: 10% improvement in what?

The Advanced Design Director (Europe) simply says: "...improves aerodynamic efficiency by up to 10%." So I'm assuming he's referring to Cd.

The roof extension slides back by nearly 10cm at highway speeds (and also tilts up under hard braking). There's also an active spoiler/diffuser under the bumper:

http://ecomodder.com/imgs/saab-9x-bi...ctive-aero.jpg


What's interesting is that there appears to be gaps between the extensions and the surface they extend from, creating slots. Presumably airflow would be drawn through the slots, top and bottom, by the lower pressure behind the car.

Toyota has been putting these on its hatchbacks, SUVs and minivans for years. It doesn't have to be active. It just has to work in the wind tunnel. The gap splits the air cascading off the roof onto the back of the vehicle in order to spread out the pressure gradient and reduce turbulence.
http://www.autoall.com/images_products/as-1723A.jpg

http://www.toyota120.com/assets/imag...ar_spoiler.jpg

http://www.autoall.com/images_produc...YOTASIENNA.jpg

http://parts.donjacobsscion.com/imag...na_Spoiler.jpg
And people thought they were just for looks.

I think the second image looks more like one of those "keep the rear window clear" devices, rather than a drag reduction device.

Anything that sticks up higher than the trailing edge of the roof would be dubious as a drag reducer.

Yeah the second one is a 4runner which doesn't have a rear window wiper. The rest do.

This is what I think too.

I really like what they did with the saab. They're taking it to the next level.

Crude interpretation of Fowler flap?