The Christmas Tree Effect

Our intuition is to add things to solve problems, but sometimes we should take away

Twenty-eight states have used electronic road signs that display the number of traffic deaths so far in a given year. The idea is that the signs will serve as a behavioral nudge to prompt drivers to proceed more safely. It would, of course, be nice to know if the nudge works.

On the roads of Texas, a pair of scientists found an excellent natural experiment to address that issue. The Texas Department of Transportation began using the fatality-count signs in 2012 — for just one week each month. Thus, the scientists could compare traffic accidents in the sign and no-sign conditions on the exact same roads, at the exact same time of year, at the exact same time of day, and on the exact same day of the week. The only difference would be whether or not the signs were displayed.

The duo studied eight years of traffic data, and 880 electronic warning signs. Here’s the conclusion, in an unfortunate nutshell: the fatality signs increased the number of crashes. The scientists estimated that the road-sign campaign caused an additional 2600 accidents and 16 deaths per year, in Texas alone.

Whence the backfire?

The researchers think it’s because these signs, which are meant to grab your attention, grab your attention. Like, when you should be paying attention to the road.

Psychologists use the term cognitive load to refer to the demands placed on your working memory. Working memory is basically where you can hold a small amount of info in your head briefly while doing something else. Think, for example, of looking at a phone number in your email and then trying to copy it into your phone before you forget it. You might be able to hold it in working memory long enough to get that done. But if you’re doing that and trying to have a conversation at the same time, the cognitive load may be too great for you to handle it all at once.

The researchers in this road-sign study guessed that, because the signs displaying fatality stats are interesting to look at and consider, they increase a driver’s cognitive load. Thus, the driver briefly has less brain power available to deal with driving.

They back that hypothesis up by showing that signs that displayed higher death tolls (i.e. potentially more attention-grabbing signs) caused more accidents than signs that displayed less arresting stats. They also found that the signs increased accidents more on tricky stretches of road, where drivers really need to pay attention.

Their conclusion is blessedly simple:

“Ceasing these campaigns is a low-cost way to improve traffic safety.”

Apparently, we should be taking interesting signs away, not adding them.

A larger lesson about smaller things

I was recently interviewing an Army officer who led a team that designed new body armor. Part of the impetus for the new design was the bulk of the standard equipment. Over time, the armor had suffered from “the Christmas tree effect,” the officer told me.

Specifically: for years, every adjustment had involved adding something — like hanging ever more ornaments on a Christmas tree — until the armor outweighed some smaller soldiers. So the Army reset the design process, and ultimately created a piece of equipment that was both lighter and more effective.

Like the road-sign backfire, the officer’s invocation of the Christmas tree effect reminded me of the work of University of Virginia professor Leidy Klotz. Klotz’s research spans engineering, design, and human behavior, and hammers home an intriguing finding: humans are hardwired to add stuff to solve problems, and we often overlook better solutions that involve taking stuff away.

I found Klotz’s book, Subtract: The Untapped Science of Less, really thought-provoking. I meant to do a full post on it ages ago, but it slipped through one of the many cracks in my newsletter brain. Still, the book has had a tangible impact on this newsletter.

With no space limitations, my intuition is always to cram more information into posts. But now if I find myself beginning an internal debate about whether to cut or add something, I just cut it. End of story.

It’s hard for me to say whether that has made the newsletter better. (I think it probably has; there was a Christmas-tree phase early on where it was getting ever longer and more digressive.) But having that decision heuristic has certainly made it more manageable.

The subtraction game

And now for your assignment:

In a previous post, author Daniel Coyle told me briefly about a tactic called the “subtraction game.” Here’s what he had to say:

Modern work is nightmarishly insidious about adding stuff to our plates. The cure is to get your group together and ask: What do we still do that is adding needless friction, or is no longer useful — and then stop doing those things.

Take a minute and play the subtraction game with yourself, or your team. If you come up with anything you can take away, I’d love to hear about it in the comments below.

Thanks to Jonathan D. Hall and Joshua M. Madsen for their research.

In another post, I talked with Gloria Mark, author of Attention Span, about the limits of attention. Don’t read that post while driving.

Lastly, I still hope to interview Leidy Klotz about his book, Subtract. If you have any questions about the human instinct to add, rather than subtract, to address problems, feel free to leave them below. Whenever I use a question from a reader, as I did at the bottom of last week’s post, I always give credit.

If you liked this post, please take a moment to share it.

Thank you for reading (while not driving). Until next time…

David

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