Sometime around 2009, America’s roads started to become deadlier for pedestrians. Fatalities have risen ever since, reversing the effects of decades of safety improvements for reasons that aren’t well understood.

Embedded within this trend is an even more curious pattern that could provide some clues about what has changed: Nearly all of this rise in American pedestrian deaths has come at night.

Nothing resembling this pattern has occurred in other comparably wealthy countries. In places like Canada and Australia, a much lower share of pedestrian fatalities occurs at night, and those fatalities have generally been declining.

In America these trends present a puzzle that has stumped experts on vehicle design, driver behavior, road safety and how they interact: What changed, starting about 15 years ago, that would cause rising numbers of pedestrian deaths specifically in the U.S. — and overwhelmingly at night?

In 2021 more than 7,300 pedestrians died in America — 3 in 4 of them during the hours between sunset and sunrise.

Federal data that tracks every roadway fatality makes clear the problem is not just about the behaviors and routines that happen to occur around nighttime. It is darkness itself that matters.

The deadliest time of day for pedestrians over the course of the year tracks the hour of the setting sun: Deaths peak closer to 6 p.m. in the depths of winter and around 9 p.m. in summer months.

Researchers have found related patterns looking at fatal collisions that occur in the weeks before and after clocks change for daylight saving time. When the 6 p.m. hour abruptly changes from light to dark, for example, even as traffic patterns generally remain the same, that hour becomes abruptly more deadly, too.

In the dark, pedestrians are harder to see than other road users. America’s roads also weren’t particularly engineered with this risk in mind.

“We literally taught generations of engineers to design conditions for daylight and not to consider nighttime,” said Rebecca San­ders, founder of Safe Streets Research and Consulting.

New risks

The most obvious potential risks that have changed in America since 2009 are found inside vehicles — in smartphones, in the dashboard displays, in the growing weight and force of vehicles themselves.

Smartphones have overlapped closely with the timeline of rising pedestrian deaths. Apple’s iPhone was introduced in 2007. Within a few years one-third of American adults said they owned a smartphone. By 2021, according to the Pew Research Center, 85% did.

When it comes to other sources of driver impairment, “there’s no particular reason to believe that alcohol, speeding or fatigue necessarily have changed in any kind of big way,” said David Strayer, a psychologist at the University of Utah who studies driving. “What has changed is the amount of technology that we’re surrounding ourselves with.”

Smartphones aren’t uniquely American. But there is one thing that is still distinctly so: the pervasiveness in the U.S. of automatic transmissions, which help free up a driver’s hand for other uses. Just 1% of all new passenger vehicles sold this year in the U.S. had manual transmissions, according to the online car-shopping resource Edmunds. In Europe, manual transmissions still make up about 70% to 75% of cars on the road, estimated Felipe Munoz, senior analyst at JATO Dynamics.

It’s perhaps not surprising, then, that Americans spend nearly three times as much time interacting with their phones while driving as drivers in Britain, according to smartphone data collected by Cambridge Mobile Telematics, which helps organizations track and reduce dangerous driving. In the U.S., that distracted driving typically peaks in the evening hours.

Official data linking smartphones and crashes is hard to find, though, given that police typically don’t ask people involved whether they were using phones (and those people might not answer truthfully anyway).

Beyond just display screens, new vehicles have changed to be wider, longer, taller and heavier. While researchers have pointed toward vehicle size as a factor explaining America’s high overall rate of pedestrian fatalities, several said they were skeptical it explains much of the increase since 2009. That’s because American cars were relatively large even before 2009, and the rate at which new cars replace existing ones is slow.

“In explaining the big run-up in pedestrian deaths, it’s not actually a huge portion,” said Justin Tyndall, an assistant professor at the University of Hawaii Economic Research Organization. His research estimates that the change in vehicle types since 2009 is responsible for fewer than 100 additional deaths per year. By comparison, around 3,300 more pedestrians died in 2021 than in 2009.

Similarly, ownership of smaller vehicles (like sedans, coupes and station wagons) is down since 2009. But total pedestrian deaths from these same cars are up more than 70%, suggesting the bulk of the problem cannot be attributed to increased car size alone.

The behavior of drivers inside vehicles may also have changed over this time, researchers suggest. This timeline overlaps with the rise of opioids and the legalization of recreational cannabis. But there is little research about how cannabis affects driving.

Societal change

None of the explanations so far easily account for the full rise of pedestrian fatalities in the U.S. But while less obvious than driver and vehicle behavior, changes that have happened outside the car and across American society may be just as important.

One theory is that Americans have been migrating toward the Sun Belt, including parts of the country that developed in the auto age, that have particularly poor pedestrian and transit infrastructure and that have some of the highest pedestrian fatality rates. The rise in pedestrian deaths has been nationwide, with per capita pedestrian fatality increases in 47 states since 2009. But many areas that have had poor pedestrian safety records going back decades — especially metro areas in Florida, Texas and Arizona — have also seen the greatest recent population growth.

The number of pedestrian fatalities in Florida, for example, has increased 75% since 2009, while the population has increased around 17%.

Such state population changes alone don’t explain most of the rise in deaths, however. More relevant patterns may have to do with where, specifically, people have moved within those states.

Nationwide, the suburbanization of poverty in the 21st century has meant more lower-income Americans who rely on shift work or public transit have moved to communities built around the deadliest kinds of roads: those with multiple lanes and higher speed limits but few crosswalks or sidewalks. The rise in pedestrian fatalities has been most pronounced on these arterials, which can combine highway speeds with the cross traffic of more local roads.

The rise of homelessness in many U.S. cities since about 2016 has also put a growing vulnerable population on streets in conflict with speeding cars. In 2021, 70% of Portland, Ore.’s pedestrian fatalities were among homeless people. In 2022 about one-third were, similar to recent data in Los Angeles. Such data is relatively limited and new, but other cities have also noted a rise in pedestrian fatalities among homeless people.

Individually, any of these theories seems unsatisfying. But put together, it’s clear there’s been a particularly American mix of technological and social changes over the past decade and a half, and they have all come on top of a road system and an ingrained culture that prioritizes speed over safety.

Whatever has happened over this time has reversed years of progress on daytime pedestrian fatalities, too, leading to a modest increase in deaths. Nighttime, however, has the potential to amplify many of these new risks.