Again, it was during the 90s as I said in my comment. I was in the Mannheim area. I didn’t see it online as I was physically there.
Yes, it was in 1994, but iirc, there were just restrictions on using cars with no closed- loop catalyst during ozone smog (There were still many of them around in Germany in those days ).
All vehicles, who were allowed to drive, were restricted to 56 mph, i.e. 90 km/h.
Of course, if you were returning from a longer trip by car, you were obviously exempt 😊
Still, it was rescinded very quickly, since the regulations didn’t lower ozone emissions by a significant margin.