This was how it was set up (click to enlarge).
To start with, Queue1a & Queue1b were quite long and slow moving. Basic queueing theory and resource pooling principles tell us that 1 queue for multiple servers is almost always better than separate queues for individual servers. Therefore, I was surprised to see 2 queues. Roughly 100+ people were waiting in these 2 queues combined. I waited for at least 15-20 minutes to get to the CheckBoardingPass server.
I wasn't bored though, because the second thing that surprised me was that within the same queue, one CheckBoardingPass server was processing passengers, while the other had to halt from time to time. It was because Queue2a was backed up to the server, while Queue2b&c were almost empty. After I saw how the x-rays were setup, it was easy to see that the unbalanced system was due to the 6 x-rays not being pooled together.
The effect was a long wait for all to start with in Queue1a&b, then some waited nothing at all (i.e. me) in Queue2b/c/d/e, while others waited in a lineup of 5-15 people in Queue2a/f. For the 4 CheckBoardingPass ladies, 2 of them were busier than the others, but all could feel the pressure and frustration from the passengers in Queue1a&b. For the staff manning the x-rays, this meant some were very busy processing passengers, while others were waiting for people to show up.
Also worth mentioning was that each x-ray was staffed by 5 persons: 1 before it to move the baskets and luggage towards the x-ray, 1 at it to operate the x-ray, 1 after it to move the luggage and baskets away from the x-ray, and 2 (1 male and 1 female) to search the passengers going through the gate, if they trigger the bleep. Seems very labour intensive. If they studied the arrival pattern of passengers needing to be searched, I wonder if it'd save some personnel here by pooling at least the searchers for a couple x-rays (if unions permit!).
We've had this type of problem cracked for some time now and it is surprising to see major problems still. Gatwick Airport / BAA was obviously doing quite well all the other times I've gone through. How easy it is for a good organisation to perform poorly just by ignoring a few simple queue setup rules. For example, in 2001, my master's program run by the Centre for Operations Excellence out in the University of British Columbia, in the lovely Vancouver, Canada, did a very good project with the local Vancouver International Airport (YVR) on just that. The project used simulation to come up with easy-to-follow shift rules for the security line-ups so that 90% of the passengers would wait for less than 10 minutes to go through. In fact, the project even caught the attention of the media, and was broadcasted on the Discovery Channel (how cool is that, and how fitting for OR work). Watch it here. Now come on, BAA, you can do better than this.
Security Screening: Bottleneck Analysis (a mathematical quantification of the inefficiency)
Security Screening: Discrete Event Simulation with Arena (a quantification of the inefficiency through simulation)
Update (9 Oct 2010):
in this article, we erroneously stated that the airport operator was BAA (British Airports Authority). In fact, BAA was forced to sell Gatwick to please regulators seeking to break a monopoly on UK's airports. Our apologies to BAA. The current owners are Global Infrastructure Partners, who also owns 75% of the London City Airport.