I just came back from IFORS17, which was a fantastic conference in a great venue (and I'm glad that many people showed up for my early-morning talk on binary optimization and R&D portfolio management), but for today's post I wanted to write something quick about the new TSA queues at the airport. In academia we talk a lot about queues like M/M/1 but I don't think there is a name for the queues in the new TSA system. (Maybe TSA is a queueing pioneer! It creates queues we academics have never imagined in our wildest nightmares.) If you know the names for the queues described below or any literature that supports their use, I'd love to hear about it.
Now there are two tracks in front of the X-ray machine, one divided into 5 "stations" where people put their stuff in the new bins and one parallel to the first one that actually feeds into the X-ray machine. The idea is that once you have your bin ready, it is going to go onto the main track that goes into the X-ray machine. It happens because "someone" pushes the bin forward onto the main track. The thing is, that someone isn't the traveler. The TSA agent wants to do that, perhaps to avoid having people knock other people's bins while they try to push theirs, but then travelers who arrived long after you could have their bins move forward long before yours.
If you have to put your stuff in more than one bin (even your rollerboard has to go in a bin, so it's likely you'll need more than one, although the new bins are very large), the bins are going to get separated from each other because your stuff goes in line on the main track for the X-ray machine when the agent feels like letting it get in line. This is not a good thing.
Also (1) the TSA agent at EWR kept saying laptops in a bin by themselves but the bins are enormous and since your stuff is going out of order it becomes really easy for someone else to take your laptop by mistake (it also went against the pictures I'd seen at DFW about how to properly pack the new bins - the important point is that nothing should be above or below the laptops but there can be things around them - but I wasn't going to argue with TSA) and (2) several lines of people at EWR had to merge into one line for the X-ray machines; at DFW people do "alternate merge" like it's second nature but at EWR you have people who just stare at the line and hope someone will be nice to them and (3) it's not FIFO anymore because you take the first available station by the X-ray, even if that station is closer to the X-ray machine than the station of people who were in front of you in line.
I liked the old system a lot more. I particularly liked the FIFO part because it seemed fair. Sadly, I've seen the new approach both at EWR and DFW, so I'm assuming a nationwide rollout. I just hope whoever came up with the new way of doing things wasn't an engineer. It's suboptimal by a wide margin.
Ok, so here is the mathematical description. You have 1 X-ray machine, 2 lines of travelers that attempt to merge into 1 line to use the X-ray machine, 5 stations, 1 parallel track where the bins are later pushed onto to get Xray'd. The traveler goes to the first available station. Then he has to wait until his stuff goes onto the X-ray track, and if he has multiple bins he has to wait until he found a way to squeeze the last one in, then he queues for the metal detector, then he waits for his stuff to come out of the X-ray machine. Remember that the TSA agent, not the traveler, decides when the traveler's bins go on the X-rays track (the TSA agent makes the gaps between bins to let a new bin come onto the track). Therefore, people who came to available stations after the traveler might have their stuff pushed into the X-ray machine first and might go through the metal detector before the traveler. Compute the average time to go through security and compare with the average time in the old system. Also compute a new criterion called the Traveler's Sense of Shock and Disbelief at TSA's New Ideas, alternatively called "Did someone get paid to come up with this?", surely to be the focus of a case study either about the crazy things people come up with to justify their consulting gigs or the flaws in the decision processes that green-lighted this innovation. Discuss.
I suppose whoever came up with this disliked having to wait behind, say, families with young children who had to take off their shoes, or elderly people who moved too slowly for their taste. It still seems there would be better, simpler ways to address this, starting with having more lines open so that people can move away from a slow line toward one that goes faster.
Maybe the lines should be per type of customers (although I'm not sure if travelers would comply if they're in a rush and another line goes faster, but perhaps having TSA lines matching the group numbers of the airlines, such as A/B/C for Southwest or 1/2/3/4/5 for United would be aligned with travelers' frequency of travel and presumably their familiarity with the screening process), or the lines could be based on the amount of luggage travelers have to screen (do they have a laptop, do they have a rollerboard) - something similar to the express checkout lane at the supermarket.
Or there could be a system where travelers don't enter the line to the X-rays until their stuff is in bins. (If we allow ourselves to dream for a second, TSA could invent a cart that carries multiple bins to the X-rays. Heck, it could be the X-ray machine of the future: a cart robot that has all your things neatly arranged on the cart and drives itself to the X-ray machine, and then the X-ray machine would be able to scan your things one by one, and your cart would re-appear at the other end of the machine, and then you could happily push your cart to the gate or return it at the checkpoint.)
It'd also be interesting to have a system where people can see the average time to go through security at different times of the day at their airport and the current real time, like what Google does for restaurants, although for airports we also need to have a measure of the staffing level to be able to compare numbers.
If TSA was serious about decreasing waiting times at checkpoints, it would run a nationwide competition among universities (or at least industrial engineering departments) to suggest improvements that would be a bit more thought-out than this. I bet students could come up with a better alternative using IE/OR tools. In the end, just thinking I might have to go through the new screening system every time I go to the airport makes me very uneager to fly, and perhaps that's the point.