Work continues on the Silver Line project in Tysons Corner earlier this year. (Nikki Kahn/THE WASHINGTON POST)

Metro officials’ decision to extend the new Silver Line was necessitated, in part, by safety concerns, according to a report the agency is expected to release Thursday.

Officials are expected to tell the Metro board’s Customer Service and Operations Committee that they will need an additional $4.6 million in the first year as part of the revised Silver Line plan.

Metro officials offered additional details Wednesday about the revised Silver Line plan, and they said the new configuration will be in effect when the line goes into service, as early as the end of next year.

Officials said they have decided to extend service to Largo rather than have it terminate at the Stadium-Armory station as originally envisioned. That change is expected to cost $1.4 million. The rest of the increase is a result of additional staff and electricity costs associated with running trains more often than previously planned on the Silver Line — as well as on the Blue, Green, Yellow and Orange lines.

The change is needed because of concerns about safety, according to the report. A pocket track that would have been used to reverse the train is on an elevated structure about a mile from Stadium-Armory, and it can’t be retrofitted with switches the National Transportation Safety Board has recommended that Metro install to prevent derailments.

Adding to the difficulty, the pocket track is among the shortest in the system. Although it can accommodate an eight-car train, Metro officials determined that turning trains would require a level of precision difficult for all but the most skilled operators. In addition, trains would have to slow as they approach the switch, which would have a ripple effect for other trains along the route.

Metro officials last reviewed the Silver Line service plan in 2004. Metro spokesman Dan Stessel said it was only in recent months, after a new review began, that officials raised concerns about the pocket track at Stadium-Armory.

“We are in a different place as it relates to safety, and we’re always going to err on the side of safety,’’ Stessel said. “That’s what building a safety culture is all about.”

The shift in service would require about 24 additional rail cars, which Metro officials say can be pulled from the existing fleet.

As a result of the service shift, when the Silver Line opens, officials will end Orange Line Rush Plus service, in which trains travel to New Carrollton and Largo during rush hour. The service, launched in June, funnels extra trains to selected stations during rush hour. Silver Line trains will replace Orange Line Rush Plus trains. Rush Plus service will continue on the Yellow Line, Stessel said.

Silver Line trains are expected to run every six minutes during peak times and every 12 minutes at other times, the report said.

The first phase of the $5.6 billion Silver Line rail, which will extend Metrorail service from East Falls Church to Wiehle Avenue in Reston, is expected to be completed in August.

According to estimates released in October, Metro officials think Silver Line ridership will top 14 million in its first year of operation. They estimate that additional fare revenue from the Silver Line will be about $2.8 million a month, a figure that takes into account new and existing passengers. Northern Virginia officials believe the rail line will spur economic development along the corridor and provide a critical transportation alternative.