10 July 2007
There’s something about traveling that makes me think about interaction design. Maybe it’s all the signage and status updates and checkpoints. It feels like a physical representation of software (usually really bad software).
Recently I learned a few things about interaction design and user experience from waiting in lines at the airport. Nothing groundbreaking, but it’s interesting to confirm what you know by seeing it play out in another context.
Lesson one: A small increase in efficiency for all users has a more significant impact on overall performance than a large increase for a small percentage of users.
I never check my bags when I fly because of those “express” check-in kiosks. Almost every major airline has them now. I just get to the airport an hour before my flight, print my boarding pass and get in line for security.
With the big airlines, there is always a huge line to check in with bags. There’s never a line for the kiosks marked “no checked bags.” I blame all the security restrictions on what you can’t take on planes. I’d rather pack my shampoo in a plastic bag than stand in line for an extra half-hour. Most people don’t think about it that way I guess, so, shorter lines for me. Hooray.
Ten items or less
This is a classic example of the “express lane” method of increasing efficiency. I make a small sacrifice (packing light and carrying on) and in return I get to jump the line. It works great as a quick fix for a slow process, but only for a small percentage of users. For that small group of users, the increase in efficiency is very high, but it comes at the expense of all the other users of the system. The bigger the line for checked bags, the faster I get through the express lane. If everybody did the same thing, the lines would be just as long for everybody, and we’d all be back where we started.
But that’s the big boy airlines. This time I flew Southwest. The express lane trick doesn’t work with Southwest because everybody knows you just check in online and print your boarding pass at home the day before your flight. Because more people know they don’t have to wait in line to check in, more people choose not to wait in line to check their bags either.
So when I got to the airport, I blew past the check-in counters and headed straight for the security line. And I followed it all the way to where it ended, somewhere on the other side of baggage claim. I almost panicked. (“I don’t belong here!”) I looked around frantically for the express lane, but this was it. When everybody’s in the express lane, guess what? There is no more express lane.
Just as I started muttering to myself, the line started moving. And it kept moving. Before I had a chance to get over my inflated sense of entitlement, I was halfway across the baggage claim. I was through the whole line and putting my shoes back on at the other side in less than 20 minutes. It wasn’t exactly rocket fast, but it was steady. I don’t think I’ve ever seen an airport security line move that smoothly.
What impressed me most is that not only was the wait time completely acceptable (even if I had arrived less than 30 minutes before my departure time I could have made my flight), it was the same for everyone. This was a peak hour in peak travel season and nobody had to wait an unreasonable—or even uncomfortable—amount of time.
Express or excess?
So which is better, improving the whole process to get everybody through as quickly as possible, or a quick fix to get a few people through marginally faster while subjecting the rest to the same long waits? More importantly, which is more sustainable for a fast-growing system? What happens when you double, or triple the number of users? Which one breaks down first? Maybe the big airlines aren’t worried because they’re not growing users very fast—or at all.
Even supermarkets (the classic express lane environment) are learning the same thing, and are consolidating many lines into a single, faster-moving line. The results, according to this NY Times article about Whole Foods are shorter average wait times for everyone. The same principles come up in modern research on optimizing traffic. A recent
Berkeley study of San Francisco traffic” indicated that adding carpool lanes may actually contribute to congestion rather than reduce it.
These results are interesting because they go against how we naturally think about optimization—it’s counterintuitive. We see long lines and we think long waits. So we try to make the lines shorter, instead of making them move faster. But as is so often the case, it turns out our instincts are wrong because our intuitive mental model is flawed.
What are are the implications of this kind of thinking about optimization when applied to network systems like the Web? Should the FCC be asking the CEO of Southwest and Whole Foods about net neutrality?
What about our own apps? What can we learn about optimizing their performance, or even perceived performance? Which leads me to the other thing I noticed in the airport security line.
Lesson 2: In order to get the maximum benefit from increased efficiency, it should be visible as early in the process as possible.
It struck me how hard it was for people (myself included) to get over the initial impression of seeing the ridiculously long line. Everybody had the same incredulous, panicked look on their face as they saw how far they had to go to get to the end.
Once we were in the line and realized how steadily and quickly it was moving, the panic subsided. But it took three or four airline employees to reassure people just joining the line and convince them to stay instead of milling around looking for other options. And even after telling everyone repeatedly that the average wait time was about 20 minutes, they still took a lot of abuse from passengers who had a hard time believing them.
No matter what you do to improve the efficiency of a process, you’re going to waste effort or lose users the longer it takes for users to see the benefit. People expect things to be slow, especially on the Internet. If you can convince your users up front that your process is going to be quick, simple and painless, the whole process will be that much more efficient. The perception of efficiency is almost as powerful as the real thing.