I've seen the two level queue in use at some airports for security and immigration. But they do have a person splitting the head of the long queue into the sho

I've seen the two level queue in use at some airports for security and immigration. But they do have a person splitting the head of the long queue into the short queues immediately in front of each x-ray machine/agent. It works pretty well, but can still be a little frustrating when you see a person who was behind you in the main queue get through first because your sub-queue took longer. People usually won't act to optimize for the best throughput, just minimize their relative wait times. The behaviour of drivers on congested roads tends to confirm this.