Reuters

In ways that aren't always obvious.

It's easy to forget, when we talk about road safety improvements in countries like the United States, that the picture looks dramatically different in many other parts of the world. Generally speaking, the more developed a country's economy, the safer its roads, although this relationship is a product of more than mere engineering.

The higher the typical income level of a country, the more likely it is to have mandates for seat belts and air bags, penalties for unsafe drivers, safety assessments for new cars, laws against cell phone use while driving, and legal maximums for blood-alcohol concentration. Higher-income countries are also more likely to have national road-safety strategies, and policies promoting walking and cycling, or encouraging investment in public transit. And that's to say nothing of the quality of medical care after a collision.

Recent national-level road safety statistics from the World Health Organization support these trends. But it's easiest to appreciate them with a look at a couple of the implications drawn from an analysis [PDF] of that WHO data by the University of Michigan Transportation Research Institute's Michael Sivak.

The below charts, built with Sivak's data, break down 170 countries by the three income categories defined by the WHO. In low-income countries, the gross national income per person is less than $1,006; in middle-income countries, it's between $1,006 and $12,275; in high-income countries, it's more than that.

The first chart illustrates that the number of vehicles inevitably increases with income...

...while the fatality rate per million vehicles decreases:

The same relationship is true of the share of pedestrian fatalities out of all road fatalities. This trend line offers a reminder that the problem of pedestrian deaths that's receiving growing attention in the U.S. is unfortunately even worse elsewhere:

Interestingly, the overall fatality rate per person (not per car) looks different from all of the previous charts. It's more an inverted U-shape function of income level:

That's not a quirk in the data. That U-shaped relationship is consistent with other studies. Sivak explains it this way:

At low-income levels, the increase in motorization is steeper than the improvements in road safety per vehicle. Conversely, at high-income levels, the increase in motorization is shallower (approaching saturation) than the improvements in road safety per vehicle.

In the Dominican Republic, new cars (and drivers) are entering the roads at a faster pace than the country's efforts to regulate safety. In the U.S., we're actually seeing trends in driving decline, as the government continues to roll out new safety initiatives.

Top image from Acapulco: Jacobo Garcia/Reuters.

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