Chains hang between old Metro cars in Washington on June 20. When WMATA purchased new 7000-series trains, they were not outfitted with chains between cars -- unlike earlier versions. (Bonnie Jo Mount/Washington Post)

Federal regulators are forcing Metro officials to take immediate action to retrofit the transit system’s fleet of 7000-series trains with new safety devices after a blind passenger fell into the gap between two train cars and onto the tracks last month.

In a letter sent Friday to Metro General Manager Paul J. Wiedefeld, the Federal Transit Administration mandated that Metro officials must install a second set of “between-car barriers” to hundreds of the new stainless-steel rail cars by Dec. 31 or risk having 25 percent of their federal funding withheld.

FTA’s letter also mandates that Metro may not introduce any new trains into the system until they are outfitted with chain guards protecting the gap between rail cars. The devices would augment rubber barriers that are already in place.

Metro officials must respond to the FTA’s letter by Friday, outlining a plan for how they intend to complete the required work on the 7000-series rail cars by the deadline.

Federal officials and people within the disabilities community have identified the design of the existing between-car barriers as a safety hazard since January 2016. In July 2016, a visually impaired male passenger fell into the gap between train cars.

In October 2016, Metro officials said they were confident that the design was safe but said they planned to install additional protections by the end of 2017.

No physical fixes have been made.

The FTA’s latest action was prompted by an incident on May 25, when a visually impaired woman using a white cane fell into the space between two train cars at the Van Ness-UDC station.

Ron Holzer, a spokesman for Metro, said the woman sustained minor injuries. She was helped back onto the platform by people who had been waiting for the train. They told the train operator what happened, and the operator notified supervisors.

“This accident highlights the ineffectiveness of the rubber barriers on WMATA’ s 7000-series rail cars in mitigating safety risks for passengers with visual impairments,” Henrika Buchanan, an acting associated administrator of the FTA, said in her letter to Wiedefeld.

Metro officials continue to say that the current design is safe but that they will take additional steps.

“We remain confident in the safety, accessibility and compliance of the design with all applicable law,” Holzer said in a statement. “While our testing confirmed the safety of the current design, after consulting with our customers and the FTA, [Metro] will replace the existing between car barriers with chain-barriers on the 7000-series currently in passenger service.”

On Metro’s older train models, chains hang in between every set of train cars, to stop people from falling into the gap.

On the newer trains, some of the gaps between train cars are guarded with stiff rubber barriers. Those barriers are recessed nine inches from the edge of the platform, just enough space to allow a person to step into the gap between the trains and fall onto the tracks.

The FTA wants Metro to return to the older chain design on all rail cars.

“The rubber barriers create inconsistency in WMATA’ s [between-car barrier] system, which can be difficult for passengers who are blind or have low vision to recognize,” the FTA letter said. “They also are more difficult to detect with a cane, being recessed from the side of the railcar further from the platform than the chain barriers. In addition, unlike the chain barriers, the rubber barriers leave as much as a nine-inch gap at the platform level, which can be mistaken for an opening.”

That’s exactly what happened two years ago, when David Kosub, a federal employee who is blind, tried to board a train at the Grosvenor station during the midday commuting lull. He walked into the space between two train cars, thinking he was walking into a doorway.

He fell onto the tracks and landed on his feet, the platform coming up to his chest. He screamed for help, but no one heard him. Kosub was able to push himself out of the space between the train and scrambled onto the platform just moments before the train left the station.

Holzer said that the extensive testing process for new between-car barriers has held up the process of introducing them to the fleet.

“We are working as quickly as possible with the rail car manufacturer to install the chain-barriers on the existing 7000-series rail car fleet as well as on new rail cars from the manufacturer,” he said.

In the meantime, he said, Metro has been broadcasting announcements to passengers, warning them that if they have visual impairments, they should tap on the floor of the train with their canes before attempting to board.

But Kosub, 37, continues to be befuddled at why Metro officials appear to be dragging their feet on a solution.

“It always seemed like this was an exceptionally simple fix for an exceptionally scary problem,” he said.

He said that he has offered several times to meet with Metro officials to discuss the incident and offer advice on a design fix but that they have not taken him up on it.

Kosub commutes to work by Metro every day and shudders when he thinks about what could have happened if he wasn’t able to push himself out of the hole between the two cars before the train left the station.

The incident has made him extra careful whenever he’s boarding a train — placing a hand on the doorway and always boarding in an area of the platform close to crowds of people who could help him if he made the same mistake. Retrofitting the trains, he said, would make him feel safer.

“I’m glad FTA is at least forcing Metro’s hand,” he said.