Despite increased consumer awareness of safety and a growing number of cars on the road with crash-avoidance technology, pedestrian deaths in the U.S. are at their highest level in 20 years. One reason for the increase: Smartphones.

According to data [PDF] compiled by the Governors Highway Safety Association, a nonprofit that represents the highway safety offices of the states and territories, the total number of traffic fatalities in the U.S. increased 6% between 2010 and 2015, but pedestrian deaths increased by 25% during that same time period.

Preliminary figures for 2016 put the number of pedestrian deaths at 5,997 — an 11% increase over just the year before and the highest number of pedestrian fatalities in two decades.

So what has happened in recent years that could explain this tragic increase?

There are several factors that contribute to the number of cars and people on the road, like the economy, and fuel prices. The healthier the economy, the more people drive — both for work and pleasure. And the report acknowledges that Federal Highway Administration numbers show recent increases in motor vehicle travel on all roads and streets.

Then there are those things that aren’t part of the ups and downs of economic cycles.

“A more recent contributing factor may be the rapidly growing use of smart phones to access wireless data while walking and driving,” explains the report, saying these devices can be a “significant source of distraction for both pedestrians and motorists.”

The author of the report found the increases in pedestrian deaths over the last few years “shocking.” He has been in the field for decades, and year after year of increases in fatalities is unprecedented — especially since our cars and roads have, in general, been getting safer.

“The why is elusive. We don’t know all the reasons,” Richard Retting told CNN (warning: auto-play video at that link) “Clearly lots of things are contributing. But not one of these other factors have changed dramatically.”

Want more consumer news? Visit our parent organization, Consumer Reports, for the latest on scams, recalls, and other consumer issues.