On Monday, the nascent self-driving vehicle sector reached an unfortunate milestone when, for the first time, a self-driving car killed a pedestrian in Tempe, Arizona. This also means robot drivers are becoming more like their human predecessors—who kill thousands of pedestrians every year.
And that number has risen dramatically in the past several years. In 2016, cars hit and killed nearly 6,000 pedestrians. That’s a serious spike from the historic low—below 4,000—in 2009.
The Great Recession explains some of the fluctuation. When fewer people have jobs, they spend less time out and about, and their exposure to potential crashes drops. When times are good, the opposite happens. “Economic changes do give us a good idea of the general direction of traffic deaths,” says Richard Retting, the general manager of Sam Schwartz, a New York City–based traffic engineering firm. But the American economy’s steady recovery can’t account for the 50 percent climb in pedestrian fatalities in the space of a few years.
OK, how about other factors? Demographics matter. “We know that a 60-year-old person hit by a car is more likely to die than a 25-year-old,” says Laura Sandt, the director of the Pedestrian and Bicycle Information Center at the University of North Carolina. She says her team factors in things like time of day and the weather—both of which might influence visibility and behavioral choices, like whether or not a person might be drunk. Intoxicated drivers and pedestrians are more likely to be involved in fatal crashes.
Then there are design factors, like the speed limit. Faster cars are more likely to hit, and kill, slow, soft bodies. “In a lot of places where pedestrian crashes occur, the road isn’t inherently safe for all modes of travel,” says Sandt.
The federal Department of Transportation started tracking pedestrian traffic deaths in 1975, and the early numbers painted a stark picture. In 1979, the all-time high, cars killed more than 8,000 pedestrians. In the ensuing decades, activists have pushed those in power to make the streets safer, with policies like lower speed limits, more crosswalks, and stiffer punishments for drunk drivers.
“From the high in 1979 to 2009 we’ve cut the number in half, which is nothing short of remarkable,” Retting says. And look, the decline wasn’t steady. Economics has always maintained its tidal hold over the ebb and flow of pedestrian safety, and politicians seem perennially inclined toward infrastructure that favors cars. But the upward trend in pedestrian safety seemed inexorable.
That is, until 2010, when pedestrian fatalities jumped back up. And then kept climbing. “Something remarkable has happened to cause this other than the economy improving,” Retting says. He says he has looked at every variable he can think of, but none explains numbers that he describes as “jumping off the graph.” The US has experienced economic booms without such dramatic jumps in pedestrian deaths. And while more people are taking public transportation (and thus spending more time on foot), Retting has looked at data from numerous public transit agencies, and says those don’t hold the answer either. “I’m not sitting here with a smile on my face saying this is some great research opportunity, either,” he says. “I’d like to put out a report, but we just don’t have enough data.”
He suspects the spike in deaths may be coming from a factor outside his discipline’s regular datasets: smartphone use. Between 2010 and 2016, the number of smartphones in the US increased from 78 million to 262 million. In the same time period, annual wireless data use rose nearly 400 percent.