Why do traffic deaths fall in recessions? Dangerous drivers drive less

During economic downturns like the recent Great Recession, auto fatality rates fall. The common-sense explanation for that phenomenon is that in tough times, companies cut jobs (reducing the number of commuters), and consumers buy fewer goods (reducing the number of big-rigs and other cargo vehicles on the road).

But researchers Clifford Winston and Vikram Maheshri weren't happy with common-sense explanations. They took a deep dive into a wide range of data and discovered that the economy doesn't have much of an impact on the total number of miles driven, but it does affect the mix of drivers on the roads. Specifically, dangerous drivers drive less frequently during downturns, while safer drivers drive more.

Behind the numbers

Winston and Maheshri began by looking at some facts. For example, during the Great Recession, the number of auto fatalities decreased dramatically.

Fatalities had been falling fairly steadily since the 1980s, but year-to-year improvements were usually in the one- or two-percent range. In 2008, though, auto fatalities in the U.S. fell by a whopping 11 percent. In 2009, the number of deaths fell by 9.7 percent.

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As the U.S. economy has recovered, the drop in fatalities has been more modest. In 2012, there was even a 2.6 percent increase in fatalities. And though the numbers for 2015 are still being crunched, indicators suggest that number of deaths jumped 7.7 percent above 2014.

But those numbers don't directly reflect the ups and downs of unemployment numbers. So, what's the correlation?

Winston and Maheshri discovered that during the Great Recession, some groups of drivers drove less frequently, including:

• Drivers who had recently filed accident claims

• Drivers 60 and older

• Drivers in one- and two-person household (generally meaning no kids)

• Drivers of cars that were five years old or older

Statistically speaking, these groups represent some of the least safe drivers. Why would they travel less during recessions? According to Winston and Maheshri, "One possibility is that a correlation between less safe drivers and risk aversion is reinforced by economic downturns." In other words, financial crises make the public worry more, and that worry has an effect on driving habits.

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No matter what the reason, the fact is, drivers like these drove less frequently, and that in turn had an effect on auto fatalities. In fact, Winston and Maheshri calculate that for every one percent rise in unemployment, traffic fatalities fall by an average 14 percent.

Interestingly, though, the economy doesn't have a significant effect on the number of miles that U.S. drivers travel as a whole. That's because while dangerous drivers drive less, safer drivers drive more. Those drivers include:

• Drivers between the ages of 30 and 50

• Drivers of SUVs and pickups

Why would they drive more? Again, Winston and Maheshri have a theory:

"[T]he recession could...induce some people to offset a potential loss in income by increasing their work effort, which could include taking jobs that involve longer commutes to work by automobile, taking an additional job that requires more on-the-job driving, and so on."

As with their theory about why unsafe drivers drive less frequently during downturns, this is just a hypothesis. Winston and Maheshri's goal was to look at correlations. It's up to other researchers to explain them.

The case for autonomous cars

In closing, Winston and Maheshri use their findings to argue for the adoption of autonomous cars. Their reasoning goes something like this:

• Dangerous drivers pose real safety risks and negatively affect the nation's productivity.

• However, prohibiting dangerous drivers from getting behind the wheel is unfeasible and could also cause productivity to fall.

• Therefore, it's in America's best interest to put the most dangerous drivers in autonomous cars, keeping the economy strong and other drivers safe.

It's a bit of a non-sequitur, but we see what they're getting at.

If you'd like to read Winston and Maheshri's paper in its entirety, grab your slide ruler and download this PDF.