It's a dangerous world for pedestrians, and smartphones aren't helping.

A new report estimates that in 2016, the United States saw its largest annual increase in pedestrian fatalities since such record keeping began 40 years ago.

"This is unprecedented and, quite honestly, shocking," Richard Retting, the report's author, told CNNTech. "I've been in the highway safety field 35 years, we just don't see record increases, let alone consecutive years of record increases."

The Governors Highway Safety Association estimated there were 6,000 pedestrian deaths in 2016, the highest number in more than 20 years. Since 2010, pedestrian fatalities have grown at four times the rate of overall traffic deaths.

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"The why is elusive. We don't know all the reasons," Retting said. "Clearly lots of things are contributing. But not one of these other factors have changed dramatically."

The thing that has changed dramatically in recent years is smartphone use. The volume of wireless data used from 2014 to 2015 more than doubled, according to the Wireless Association.

Drivers and pedestrians who are distracted by their smartphones are less likely to be aware of their surroundings, creating the potential for danger.

"Somebody staring at their phone for two seconds at 40 mph has covered a very long distance," Retting said. "It's not hard to imagine a pedestrian at the wrong place, wrong time, never being seen by the driver."

Most pedestrian fatalities occur at night in road space designated for vehicles. Only one in five pedestrian fatalities occur at intersections.

Related: Traffic deaths expected to cross troubling milestone

The Governors Highway Safety Association looked at data from the first six months of 2016 that came from 50 state highway safety offices and the District of Columbia. The complete data will be available later this year.

The findings come as traffic safety experts have called for totally eliminating deaths on roadways. Near-term solutions include designing roads and vehicles to be safer. Cutting down on speeding and drunk driving are obvious targets.

The most impactful solution may lie over the horizon. Car and tech companies are investing billions in autonomous vehicles. Once ready, experts anticipate self-driving vehicles will dramatically reduce the 1.25 million motor vehicle deaths on global roads each year.