The number of pedestrians killed on U.S. roads last year was the highest in 28 years, an increase due in part to driver and walker distraction, alcohol and drug impairment and more SUVs on the road, a safety organization report says.

Using data reported by states for the first half of 2018, the Governors Highway Safety Association estimates that 6,227 pedestrians were killed last year. That's up 4 percent from 2017 and 35 percent — or more than 1,500 additional deaths — from 2008.

The association says more people are walking to work and they're more distracted by smartphones. America's massive switch from cars to SUVs and light trucks caused more deaths because the taller SUVs tend to hit pedestrians in the head and upper torso, causing more severe injuries, the report said.

"At the same impact speed, a pedestrian is much more likely to die in an SUV crash than in a car crash," said Richard Retting, a consultant and former top traffic safety official with the city of New York who authored the report. "Even at 20 or 25 miles per hour, being hit by an SUV, the chance of fatal injuries increases significantly."

The number of pedestrian deaths involving SUVs rose 50 percent from 2013 to 2017, while passenger-car-related deaths increased by 30 percent, the study found. The number of walkers killed by passenger cars was still higher in 2017 at 2,279, but SUVs accounted for 1,097 deaths.

Pedestrian deaths had been declining for decades until 2009, when smartphone sales and data use began to spike, Retting said. While Retting said the correlation between the two needs to be studied more, phone use is one of the only variables that could cause the increase in deaths. "Cellphone use is one of the few metrics I can find that shows a consistent change, a large scale change, year after year," Retting said.

In about half the fatal crashes, either the driver or the pedestrian was impaired by alcohol, with blood alcohol levels of 0.08 grams per deciliter, the study found.

The report also says most deaths happen on local roads at night and away from intersections, and it called for safer road crossings. Night pedestrian fatalities increased by 45 percent from 2008 to 2017, while daytime deaths rose a much smaller 11 percent.

Retting said municipal governments should evaluate pedestrian crossing patterns and consider installing crosswalks and lights even if there's no intersection.

The increase in pedestrian deaths from 2008 to 2017 came as overall traffic deaths fell 6 percent, the report said.

It also called for law enforcement and safety education campaigns to make sure drivers and walkers can safely coexist, as well as for road safety audits.

It said that 23 states saw declines in pedestrian deaths during the first half of last year, with six states reporting double-digit drops.

Retting said he expects pedestrian deaths to fall as more SUVs and cars are equipped with automatic emergency braking and pedestrian detection systems. Most automakers in the U.S. have pledged to make automatic braking standard across their lineups by September of 2022.