Passengers make their way in and out of a 7000-series Metro rail car on Feb. 7, 2018, in the District. (Salwan Georges/The Washington Post)

Metro is speeding up work on safety improvements in its fleet of 7000-series train cars after federal regulators threatened to withhold millions in funding, according to a letter sent by Metro management to the Federal Transit Administration on Friday.

But it is unclear whether the new upgrade timetable — the work is to begin next month and be completed by May 2019 — will be enough to satisfy FTA officials. The agency has warned that if Metro does not retrofit cars with blind-friendly safety guards by the end of December, 25 percent of the system’s federal funding could be withheld.

“At this time we do not expect to meet the FTA imposed deadline,” Metro’s chief safety officer, Patrick Lavin, wrote in a letter to federal officials, and he urged them not to take funding from the agency.

“If the FTA chooses to exercise its authority to withhold funding, we believe this action would be counterproductive to safety and operational performance,” he wrote.

In recent months, Metro has also worried that the FTA could force the transit service to stop using the new trains if the more-than 500 rail cars covered by the order have not been upgraded by Dec. 31. Withdrawing those rail cars from service would sideline a significant part of Metro’s fleet. Metro had initially planned to finish the work by November 2019.

But FTA officials clarified this week that they do not intend to pull the trains from service if Metro does not meet the deadline at the end of the year.

The pressure from federal officials on Metro to address its “between-car barriers” — the physical safeguards intended to stop people from falling into the gap between connected train cars — has ramped up in recent months, after a 68-year-old, visually impaired woman fell onto the tracks between cars at the Van Ness-UDC station in May. The woman was pulled from the track bed and was not seriously injured.

And now passengers without visual disabilities are noticing the results of the federal pressure: For the past few months, the public address systems on trains have been playing a recording as the trains pull into stations: “This is a 7000-series train.”

The purpose of the audio messages is to alert visually impaired riders that they need to be cautious while boarding the 7000-series trains. (Metro has conducted outreach to disabilities advocacy groups, educating them about the hazards posed by the 7000s.) But the repetitive audio messages have also annoyed other riders, with some passengers complaining on Twitter that they do not understand why the transit agency feels a need to brag about the new model of train car at every stop.

The concerns about the design of the 7000s stem from when the stainless steel trains were being developed years ago. On older models of the Metro fleet, two sets of metal chains stretch across the gap between the train cars, so that anyone erroneously reaching with a cane or a hand into the gap between cars would probably detect the chains and move to a door instead.

But when the time came to begin manufacturing the 7000s, Metro officials wanted a change. The chains were cumbersome when moving train cars around the rail yard, and workers had reported slip-and-fall injuries related to maneuvering the chains during icy weather.

Instead, Metro opted for a different safety feature: black rubber flaps that stick out like tail fins from either end of each rail car. Those flaps are set farther back from the edge of the platform, which federal regulators believe is why at least two visually impaired people reportedly stepped into the gaps between the train cars and fell onto the tracks.

Those incidents alarmed the FTA enough that it issued an ultimatum: Metro must install new between-car barriers on all 7000-series trains by the end of 2018 or the system might temporarily lose some federal funding.

That threat got the attention of Metro officials. In his letter to the FTA on Friday, Lavin said the trains’ manufacturer, Kawasaki, has agreed to expedite the retrofitting.

Still, he said, there are limits to how quickly Metro can press Kawasaki to work. And in a letter from Kawasaki to Metro, forwarded to the federal government, the manufacturer explained the reason for the 10-month timeline. “The bracket assembly has a long lead time,” wrote the program manager for the 7000 series, and “the polishing process for painting takes a long time.”