highway raid

Yesterday i was travelling from Croatia to Czech republic (over night) and somewhere in Austria I experienced something I have never seen. The whole highway was closed and diverted to a petrol station / rest station, where were tens of policemen with guns and were checking each car and truck. Well we were able to continue but I was really wondering what was going on there. It was done really profesionally and what felt really crazy was the horizont of the highway how each lane was blicking with yellow light "move right arrow" and suddenly there was no lane at all only the rest station with hordes of policemen :-).