A federal review of a high-tech safety system is forcing the continued delay in commuter service, Sonoma-Marin Area Rail Transit officials say.

That safety system was installed for the first time on part of a Colorado rail line last year, but has not been completely bug-free. It has forced the Colorado rail agency to seek and receive waivers from the Federal Railroad Administration to continue running that line.

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Those circumstances may be a reason why federal officials are being methodical before signing off on SMART, rail officials have said.

“The FRA, in particular, needs to sign off on Positive Train Control,” said San Rafael Mayor Gary Phillips, a SMART board member. “That system is performing satisfactorily for SMART. We saw it work during the preview service.”

SMART has spent $50 million to implement the Positive Train Control system on the 43-mile line from downtown San Rafael to the Santa Rosa Airport. The system essentially controls movements on the rails electronically to slow or stop trains before certain types of accidents could occur.

SMART is poised to be the first start-up rail system in the country to be completely outfitted with the safety system designed to prevent potentially deadly accidents.

In April 2016, the Denver-based Regional Transportation District began using Positive Train Control on a new 23-mile spur from downtown to the city’s airport. The line has been operating on waivers from federal officials while they attempt to resolve a nagging timing issue with safety arms that is caused by integration challenges between crossing software and Positive Train Control. The waiver includes the requirement that flaggers be stationed along the line as a safety precaution.

SMART officials say their Positive Train Control is working and that they are talking to federal officials on a daily basis as they seek final approval.

“This deals with public safety and they are being cautious,” said Farhad Mansourian, SMART’s general manager, of Positive Train Control. “PTC is new. We are not an agency that has been running for 40 years. We are a new agency with brand new service.”

Tiffany Lindemann, a spokeswoman with the Federal Railroad Administration, said SMART’s Positive Train Control is getting a hard look.

“FRA is still working closely with SMART on the PTC review,” she said via email. “Although SMART is in the final stages of the review, the length of time the review can take varies depending on the complexity of the PTC system.”

In SMART’s case, Positive Train Control works via a fiber optic network used to “talk” to the train system to prevent a train from moving while sitting in a turnout, while another train passes; maintain safe speeds in curves to prevent derailments; and to slow speeds in work zones where workers are present.

The system stops the train if an engineer fails to adhere to the software-programmed instructions. The system is also used by dispatchers to lower speeds when a grade crossing has been damaged.

Such a system could have prevented the deadly accident of Amtrak passenger train 188 in Philadelphia in May 2015, National Transportation Safety Board officials said. That train had entered a curve where the speed is restricted to 50 mph. But the train was traveling at 106 mph because the engineer was distracted and failed to slow the train. Eight passengers were killed and 185 others were transported to area hospitals. SMART’s top speed will be 79 mph.

SMART will have to spend between $10 million and $12 million to operate the safety system on the downtown San Rafael to Larkspur extension that could open in 2019.

In 2008, Congress required railroads to install the safety system. In October 2015, Congress extended the original deadline to implement the system from Dec. 31, 2015 to at least Dec. 31, 2018. In theory, SMART could have delayed deploying the safety system until later to save money now.

Mansourian said SMART is close to launch.

“We can almost taste it,” he said.

The Denver Post contributed to this report.