A Circulator bus is seen at a red light in Washington on March 2, 2013. (NICHOLAS KAMM/AFP/Getty Images)

The D.C. Circulator has been struggling with frequent breakdowns of buses, resulting in interrupted service and long waits for passengers.

On any given day, as many as one-third of the Circulator’s 67 buses are taken out of service because of mechanical problems, city transportation officials said in an interview. Some buses are taken off routes after morning safety checkups, while others have broken down in the middle of their routes, leaving passengers stranded and others waiting at the bus stop. The 10-minute headway that the system promises often turns into a 30-minute wait.

The performance decline stems from years of maintenance neglect and after warnings spelled out in multiple audits about the dire condition of the fleet.

“It is a big problem,” said Sam Zimbabwe, a top D.C. Department of Transportation (DDOT) official. “We are not meeting our own targets for service and reliability.”

On-time performance this year dropped to its lowest level since at least 2012, according to data provided by DDOT, which funds the system that provides more than 5.1 million trips annually on six lines. In June, 67 percent of customers were picked up on time — better than the 52 percent in April but still below the Circulator’s minimum target of 80 percent. By comparison, Metrobus’s on-time performance in the first quarter of the year was 77 percent, just short of the 79 percent goal.

The chronic bus problems have meant buses aren’t delivering the scheduled service. By April, only about 85 percent of the scheduled hours of service had been delivered this year, a drop from of about six points compared with the same period last year.

Officials say they anticipate relief will come next month when they start rolling out 26 newly purchased buses to replace many of the system’s aging vehicles. In addition to those replacement vehicles, 14 more buses will be added to the fleet, bringing the total number of buses to 72.

Defects on the distinctive red buses have been an issue for years. A 2015 audit found that First Transit, the contractor that operates and maintains the D.C. Circulator fleet, had fallen short on maintenance. Failure to tend to wear-and-tear issues were degrading the vehicles’ useful life, the audit found.

A follow-up inspection last year found improvements yet lingering maintenance issues. And yet another audit this year concluded that a lack of skilled technicians continues to hamper the Circulator’s ability to detect problems and make repairs.

Poor oversight led to troubling safety and operational flaws, according to the audits commissioned by DDOT. The transportation agency owns and funds the Circulator, but Metro manages the contract and provides oversight of First Transit.

Sesil Rubain, an organizer with the Amalgamated Transit Union Local 1764, which represents D.C. Circulator workers, said drivers have reported problems with the fleet and have criticized DDOT for not taking steps sooner to add new buses.

“DDOT knew the fleet was antiquated, and they should have replaced it years ago,” he said.

Zimbabwe said the city agency is moving toward taking over the management of the system from Metro. DDOT plans to open up the transit contract for bids, possibly replacing First Transit when the current contract expires next summer.

Since 2015, the agency has taken a more active role in oversight, pressing the contractor to ensure that all the buses in service are safe. Officials said that is part of the reason there have been too few buses to run normal operations, but they expect things will improve as new vehicles are added.

Still, in recent months declines in performance have contributed to late arrivals at work and medical appointments and disappointed customers.

Eva Palmer, 21, was so frustrated after two consecutive days of delays on the Georgetown-Union Station route that she took her frustration to Twitter.

“I think my favorite thing about taking @DCCirculator is that it didn’t show up for 30 minutes so I had to Uber twice this week,” Palmer tweeted on Thursday. An hour later, D.C. Circulator tweeted back with an apology and an offer of a free ride pass.

Palmer, a media analyst at a consulting firm in Union Station, said she was already losing faith with the service and considering switching to Metro, a service she avoids because of similar reliability problems.

“I really want to give the Circulator the benefit of the doubt,” Palmer said. “But I am definitely seeing this becoming a trend, and it makes me nervous because that is the mode of transportation that is convenient to me.”

These days the messages from the Circulator’s Twitter feed are nearly identical every morning: #Alert: Experiencing up to 30 minutes of delay. Sometimes traffic congestion or construction is to blame, but many delays are because of bus breakdowns. The most recent audit found that on a January day, 24 buses were down for mechanical reasons, leaving only 43 buses available for service — short of the 51 needed to meet peak service requirements.

And the effect is getting to riders.

“At this point just cancel the morning routes,” Michelle Fantone tweeted Thursday, a particularly rough day for the system. She had waited 40 minutes before she called it quits. “This is pathetic and embarrassing.”

Amid a heat wave in the city this week, buses were pulled out of service because of broken air conditioning. Shortly before 9 a.m. Thursday, a Circulator bus idled on Wisconsin Avenue in Georgetown with the hazard lights on and a “NOT IN SERVICE” message displayed.

At the bus stop across the street, the number of people waiting for a Union Station-bound Circulator kept growing. Marguerite Cunningham first thought the idling bus was on a short break before it turned around. It took 20 minutes before the next bus arrived.

“When it’s working, it’s extremely reliable,” said Cunningham, who uses the bus occasionally from the Georgetown area to the K Street corridor where she goes for medical appointments. “I hope they find some relief soon.”