I believe they are there to check for Hazardous loads that have not pulled into the check area, and also ab loads that have also not pulled in. I was following a foreigner into the tunnel and he had the orange plates up, and once we had gone by the bus and before we got to the tunnel the traffic lights went red and the barriers came down in front of him. Next the green turn left filter came on. They had to put the filter light on 6 times before he got the message to pull off. No wonder the tunnel jams up as bad as it did with the booths. They should have somebody there to wave them off once they have been stopped.