State regulators have threatened to shut down Atlanta’s troubled streetcar unless the city resolves a slew of problems outlined in recent audits.

In a letter to Mayor Kasim Reed and MARTA CEO Keith Parker on Monday, the Georgia Department of Transportation gave the city until June 14 to submit plans to address 60 outstanding problems outlined in the reports. If those plans are not sufficient, GDOT said, it will order the streetcar to shut down immediately.

The city and MARTA share responsibility for the $98 million system that runs in downtown Atlanta. State and federal law requires GDOT to oversee the safety and security of rail operations like the streetcar, GDOT Commissioner Russell McMurry said.

The problems with the streetcar include poor maintenance procedures, inadequate staffing and a failure to properly investigate accidents.

McMurry said in the letter that, since the service started in December 2014, streetcar officials have failed to “provide timely, substantive and compliant responses to deficiencies identified by the department and (Federal Transportation Authority).”

In a statement to The Atlanta Journal-Constitution on Thursday, McMurry said the department expects the problems will be resolved and said GDOT “will continue to work with the city and MARTA to ensure this projects meets federal requirements.”

A MARTA spokesman referred comment to the mayor’s office. Reed spokeswoman Jenna Garland released a statement that said Atlanta has “worked diligently and cooperatively with state and federal regulators to provide the best possible service and experience for Atlanta Streetcar riders.”

“The city is committed to operating the Atlanta Streetcar safely and effectively,” Garland said. “We take GDOT’s feedback seriously and will continue to make every effort to work with the agency to address all action items by the date requested.”

Monday’s letter is the latest indication the Atlanta Streetcar has fallen short of the pretty picture its supporters painted when it opened 17 months ago. At its inaugural run, Reed called it a model for the rest of the country, an economic catalyst that would one day tie into the city’s 22-mile Beltline.

Problems surfaced even before it opened, with the price tag for completing the 2.7-mile downtown route ballooning from about $70 million to nearly $100 million.

After offering free fares for a year, the streetcar started charging $1 in January. Ridership plummeted. About 91,000 people rode the street in the first three months of this year – 48 percent less than the same period in 2015.

Last year, the Federal Transit Administration expressed concerns about the safety and operation of the streetcar. Among other things, it found defects in the streetcar's overhead electrical system, poor operating procedures, significant management and staff vacancies and failure to comply with state accident reporting requirements.

GDOT followed with its own report, which found confusion over the roles of Atlanta and MARTA in operating the system. It also found deficient maintenance, inadequate staff training and other problems.

In January, Atlanta and MARTA told GDOT they were making significant progress in fixing the problems. But Monday's letter shows GDOT officials do not share that assessment.

“The joint letter to the City of Atlanta and MARTA outlines the program requirements that have not been satisfactorily resolved for compliance,” McMurry said.

City Councilwoman Mary Norwood said she was not aware of the GDOT letter but hopes “the mayor and MARTA can get this fixed, because we have a tremendous investment going forward in this mode of transportation.”

State Sen. Vincent Fort, D-Atlanta, traced the problems to the city’s involvement in running the streetcar. He wants MARTA to operate the system and earlier this year introduced an unsuccessful bill that would have put the system under its control.

“The streetcar ought to be operated by professionals,” Fort said. “It’s embarrassing for the City of Atlanta to be in this position. It’s especially troubling when it comes down to safety issues.”