at least as far as recognition... low one hand wave, (it can vary), as you pass by one another.

The autobahn - one thing bad about the autobahn - if you're on a tour bus and hear, or spot, one of those rockets coming at you they pass by so fast you don't have enough time to make out the model. and

Last time I was on the autobahn, couple years ago, we were in a rented van headed to Garmisch from Munich, Germany. We were doing about 120 mph.... the actually fast cars were still going by so quickly I couldn't always make out what they were.