Photo by steve buttry on Flickr.

Dulles Airport built two huge security checkpoints in 2009, but somehow it still can take a very long time to get through security, especially at busy times when a lot of international flights are soon to leave. How long does it really take? Now we have some data.

Last August, Dulles installed new systems that estimate the wait time at each checkpoint. Cameras connect to computers which try to judge the wait based on the size of the line and the rate of people clearing the checkpoint. You can view the wait times on the web or a smartphone, and screens at the airport show the estimated times so travelers can pick the shorter line.

I set up a system to automatically capture the wait times every 5 minutes, beginning September 23. It’s been running for a little over 6 months now, which gives us a good set of data to analyze.

The west checkpoint is the one on the right when you’re facing the terminal. It’s closer to Daily Garage 2, and also the exit from customs, and is near the first stop on the shuttle buses. Here are the wait times across the average weekday:

Average wait at the west checkpoint for each 5-minute segment, weekdays.

There are some peaks at busy times of day, like early morning, just before noon, and especially late afternoon (when all of the flights to Europe leave), but it’s fairly consistent.

The east checkpoint, however, has far more variation:

Average wait at the east checkpoint for each 5-minute segment, weekdays.

Here, the wait times are very low except right around the peak times. This camera seems to report a minimum time of 2 minutes; even in the middle of the night, when the checkpoint is closed, it shows 2 minutes.

Any ideas why this one varies more? Is the volume of people checking in at United or other counters on that side more uneven than on the airlines with west side counters or passengers re-entering after clearing customs? Does TSA staffing vary more? Does the fact that shuttles drop people off first at the west side drive more, and more even, demand to that side?

What about weekends?

Those are weekdays. Are weekends different? Regional transportation always shows huge differences between weekdays and weekends, like Capital Bikeshare usage data, but airlines run pretty much the same schedule 7 days a week. And, in fact, the pattern is little different except the average wait time is slightly less on weekends:

Average wait at the west checkpoint for each 5-minute segment, weekends.

Average wait at the west checkpoint for each 5-minute segment, weekends.

Which checkpoint is better?

Which checkpoint should you take? The best strategy is to actually look at the monitors, but most likely it will tell you to head east unless it’s a peak time, when its lines get long:

Probability the east checkpoint has a longer wait for each 5-minute segment, 4 am-10 pm.

Shaded areas show times the probability exceeds 50%.

How big are the differences? If one is better, is that a strong difference? Especially with the real-time screens, you’d expect a lot of travelers to move toward the checkpoint with the shorter line, but apparently not enough do to keep the two balanced.

Differences in waits between the east checkpoint and west checkpoint per 5-minute segment.

This graph shows the size of the typical differences between the two. The center line is the median difference, and the darker area the middle 50% of times; as in the above chart, east usually has the longer lines during these peaks while west is worse at other times.

Still, there is plenty of time when the difference between the two is quite significant, assuming the equipment is accurate. If you have to fly through Dulles, a perfect symbol of how our nation once built great public works but now barely bothers to keep them up and makes new improvements on the cheap, you’ll already have long drives and walks to get to your gate; you might as well minimize the wait in those interminable security lines.

David Alpert is Founder and President of Greater Greater Washington and Executive Director of DC Sustainable Transportation (DCST). He worked as a Product Manager for Google for six years and has lived in the Boston, San Francisco, and New York metro areas in addition to Washington, DC. He lives with his wife and two children in Dupont Circle. Unless otherwise noted, opinions in his GGWash posts are his and not the official views of GGWash or DCST.