Car manufacturers often test their prototypes under extreme conditions, and very often in public roads. Like in this road in Mount Evans, one of the highest in US.
But in public roads any photographer could catch you or, even worse, the Google spy car could multi-catch you, like in this case. These guys rushed to cover the cars, but it was not enough. If you go through the pictures around this one, you can see quite a few Porsche prototypes.
A good catch for Porsche, no doubt.
360º picture in Google Street View
Position in Google Maps