As San Francisco reels from a recent string of traffic fatalities, new city data points to another vexing trend: a surge in the number of pedestrians gravely injured by cars.

Fifty-five pedestrians were critically hurt in crashes last year, according to the Department of Public Health. That was the highest number since city officials started their campaign to end traffic fatalities in 2014. Despite a concerted push to redesign intersections and update traffic signals, people walking appear to be in more danger of getting hit: The current figures show a sharp rise from 2017 — when 34 pedestrians were critically injured.

The burst in injuries mirrors San Francisco’s jump in traffic fatalities, while also reflecting a national trend. So far, 22 people have died in traffic collisions since the beginning of January, putting this year on track to be one of the deadliest in recent memory.

Pedestrians account for roughly 40% of 130 critical traffic injuries in the city overall. Counts for other modes, such as bicycles, were relatively stable.

To Jodie Medeiros, executive director of the advocacy group Walk San Francisco, this data represents the untold part of the Vision Zero story.

“More vehicles, more dangerous driving, and all of us (are) more at risk — especially people walking,” she said. “And we need to be talking about severe crashes, not just fatal ones.”

Epidemiologist Shamsi Soltani offered several possible explanations for the rise of injuries when she presented the new figures Monday morning, during a meeting of the city’s Vision Zero Task Force, charged with eliminating traffic fatalities and injuries. It coincides with a population and job boom, which means more people on the streets and roads. Increasing homelessness is also a factor, since people outside 24 hours a day are more likely to get hit. Another possible contributor: San Francisco residents are aging — one in five people who live here are senior citizens — so they move slower and are at more risk of getting severely hurt.

Most notably, more vehicles are on the road. The number of daily vehicle miles traveled increased by more than 630,000 miles between 2010 and 2016, with ride-hail companies like Uber and Lyft accounting for 47% of the bump.

“I’m trying to get a handle on why this is happening,” Board of Supervisors President Norman Yee said of the abrupt injury spike. It reverses four years of progress: After reaching a peak of 57 critical injuries in 2013, counts hovered in the mid-40s from 2014 to 2016, then dropped to 34 in 2017.

Since then, the numbers have ticked back up. The escalation in road mayhem continued this year, with a steady stream of headline-grabbing accidents, vigils at crosswalks and calls for City Hall to declare a state of emergency.

In addition to the explosive growth in San Francisco’s population and traffic, the city has also added another mode of travel — electric scooters — which produced a new subcategory of pedestrian injuries. Seven people were severely hurt in collisions involving these devices last year, and two were critically injured. Of the two critically injured crash victims, one was an elderly pedestrian struck by an e-scooter, Soltani said.

City leaders are advocating for ambitious, controversial policies to stop the bloodshed, including congestion pricing to manage the number of vehicles on the roads, and urban speed limits — an idea that’s hit resistance at the state level. Existing state law bases speed limits on how fast 85% of drivers are traveling through an area, giving cities little to no flexibility.

Some politicians have called for more aggressive measures. Supervisor Matt Haney wants to see designated car-free zones in the Tenderloin neighborhood he represents, which is among the most crowded in the city and the most perilous for people walking around. Haney participated in a “die-in” Friday afternoon at Golden Gate Avenue and Leavenworth Street, where a man police said was unlicensed and driving under the influence struck and critically injured a 12-year-old boy last week.

Yee said he hopes that measures the city is already pursuing — like re-engineering crosswalks to make pedestrians more visible — will make a significant difference.

For him, the fight is personal. Yee was struck by a car as it turned onto Fourth and Bryant streets in 2006, causing him to hurtle into the windshield. He spent nearly a month in the hospital.

“My neck is held together by two metal rods,” Yee said.

And the driver? “He got ticketed.”

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan