A highway is not a German Autobahn.
I think the test track is more about testing technology which will be installed at the roadside.
Elsewhere most people tend to drive at more or less at the maximum speed allowed. This makes for a very relaxed, easy albeit boring experience.
In Germany the difference in speed between the cars are a lot bigger, even in areas with a speed limit. In combination with the Rechtsfahrgebot (a law that makes driving in the right-most lane mandatory, unless you are overtaking or there is no space) you are constantly overtaking trucks and other cars, while others do so to you as well. Overtaking itself requires accelaration often time going beyond the actual speed limit so as not to slow down others too much which can be dangerous.
Furthermore you have to constantly monitor traffic so as not to be trapped on the right lane, if a larger group of cars comes up from behind, which happens frequently.
I highly doubt that current autonomous cars are capable of that to a degree, where I wouldn't be annoyed and wanted to take over. Especially at night, when it's raining, snowing, there is fog or a combination of these.
Contrast with American drivers, who will stay in whatever lane they want and/or pass at high speed in any lane they deem open.
Going 100 mph plus in the left lane on the German autobahn you'll be the recipient of flashing signals of grandmothers passing you at 120 if you don't get out of the way fast enough.
It's not as though you have to drive fast. Most people actually don't drive super fast, they stick to 130 to 160 km/h. You will only occasionally encounter someone going way beyond that. Just because there's no limit doesn't mean people drive at speeds they are uncomfortable with … extended periods at 160 or beyond make me queasy and I tend to stick to 140 or so. That also gets better mileage.
And drivers actually follow the signs. As an American driver it's an amazing thing to see.
Speed control flashes are a common sight :).