Silver Line tracks are seen stretching out from the McLean Station on Nov. 4 in Fairfax County. (Matt McClain/The Washington Post)

The announcement last week of yet another delay in the completion of the first phase of the Silver Line rail extension has raised concerns over whether the agency building it is pushing aggressively enough to get the project finished.

Officials at the Metropolitan Washington Airports Authority had hoped to turn over responsibility for the first phase of the rail line to Metro this month — a milestone that would bring the Silver Line one step closer to carrying passengers. But that changed after a series of tests in November identified issues with the software that controls a critical safety system. This is the second time in six months that the airports authority has announced a project delay.

Although the latest delays aren’t expected to add to the overall price of the project, they may prove costly to Metro. Each month of delay in passenger service costs Metro $2 million to $3 million in lost fare revenue, officials said.

Project officials would not give a specific date for when the fixes on the $5.6 billion project would be completed but said they would probably take several weeks. As recently as this summer, some officials said passenger service would begin this month.

MWAA officials sought to reassure the public that despite the new delay, the project will get done in a reasonable amount of time.

Parking spaces planned along the Silver Line

“We’re really close to the finish line now, but there are some issues that we need to deal with,” said Pat Nowakowski, executive director of the rail project.

In November, Nowakowski told members of the airports authority board at their monthly meeting that work was continuing and that completion of the rail line — one of the biggest infrastructure projects in the country — would probably come at the end of this month.

But he said it became clear that the timeline could no longer be kept after he learned the result of tests on the system Thanksgiving week. During those tests, officials concluded that changes had to be made to the software that governs what is known as the automatic train control system (ATC), he said. The software changes required will ensure that the computers that help run the system communicate clearly with each other.

The ATC system controls train movement and speed and ensures proper spacing between trains traveling along the system’s more than 200 miles of track. If a train is traveling too fast or gets too close to another train, the system will slow or stop the train if the operator does not act.

The ATC system is critical to the safe operation of Metro’s trains. It was the failure of this system to detect the presence of a train on the tracks that was blamed in part for the 2009 Red Line crash that killed nine people and injured dozens of others.

This also is not the first time that the Silver Line’s ATC system has been an issue. In June, one of the nation’s top transportation officials expressed concern about unauthorized changes made by Alstom Signaling, the contractor responsible for installing the system.

Federal Transit Administrator Peter Rogoff said he was troubled by unauthorized design changes Alstom made without consulting Metro. In addition, because of a shortage of equipment, Alstom workers allegedly moved some control boards from one monitoring station to another, which meant they were checking the same set of boards rather than new ones, according to three officials with oversight roles who spoke on the condition of anonymity because they were not authorized to discuss the matter publicly.

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Alstom officials declined to comment on the June report and their current work. Nowakowski said the recent delays are unrelated to the earlier problems.

In July, MWAA officials, citing different safety testing and other issues, announced an eight-week delay in completion of the rail line.

The latest news of more delays was enough to prompt Sen. Mark R. Warner (D-Va.) to ask whether officials at the airports authority are doing everything possible to make sure the project is finished on a timely basis, a sentiment that was echoed by two of Virginia’s other federal lawmakers — Sen. Timothy M. Kaine (D) and Rep. Gerald E. Connolly (D). This most recent announcement, Warner wrote in a letter to the airports authority’s chief executive Wednesday, “follows an unsettling pattern of project delays.”

“I agree with your assessment that safety should be the uppermost priority in guiding your efforts, but I believe that can be responsibly achieved while also adhering to an agreed-upon project schedule,” Warner wrote.

“I urge that you do everything in your power to complete the work as quickly and responsibly as possible and avoid further delays so that our region’s commuters and travelers can benefit from this crucial transportation link,” he said.

Connolly agreed.

“Having been one of the originals in supporting and advocating and sticking with this project in its many ups and downs, to have yet another delay, however brief, is a very frustrating experience,” Connolly said in an interview.

But, he added, given how long the region has been waiting for the project to be built, four or five more weeks is a small time frame, especially if it ensures that the system is safe.

Kaine called signing off on the Silver Line “one of my proudest accomplishments as governor.”

“I will always support erring on the side of caution to ensure the safety of Metro passengers, but hope something can be done to get riders onto the Silver Line earlier this spring,” Kaine said in a statement.

MWAA, which oversees Reagan National and Washington Dulles International airports as well as the Dulles Toll Road, is managing construction of the Silver Line, which will be operated by Metro. It is the first time that a new rail line is being built by an entity other than Metro.

Even after the software fixes are made, the airports authority must conduct its own tests, including one that will simulate a regular day of service and involve running 80 trains on the line during a regular Metro service day.

The two entities have been doing concurrent testing, but Metro officials said there are some tests and training that can only be done once they take over management of the rail line. That training and testing could take up to 90 days. Even if Metro takes less time, Warner said passenger service may not begin until April.

The first phase of the 23.1-mile rail project, which includes five stations and 11 miles of track, is being built by Dulles Transit Partners, which is led by international construction and engineering giant Bechtel. Four of the stops will be in Tysons Corner and one in Reston at Wiehle Avenue. Preliminary work on the second phase of the project, which will have six stops, including one at Dulles Airport, has begun and is expected to be completed in 2018.

For their part, Metro officials said they were not concerned by the delays. Even so, long delays could be costly for the agency, where revenue is down. But in recent conversations, officials at Metro played down the financial impact.

Metro spokesman Dan Stessel said that when budget planners began drafting the fiscal 2014 budget, they kept in mind that the Silver Line might not open as originally scheduled.

A delayed opening “will not have a major impact in the context of a $1.6 billion budget,” Stessel said, noting that Metro loses $2 million to $3 million when the system shuts down for a snow day. “In a budget the size of ours, there are always knowns and unknowns.”

Still, opening the Silver Line could offer the beleaguered transit authority a much-needed boost. In recent months, Metro has been the subject of criticism for service interruptions, including three such slowdowns on the Red Line in a two-week period.

Nowakowski urged patience: “We want people to understand we’re going to do everything we can to deliver a project that is safe and reliable — something that people can depend on and that people can feel is safe to ride.”