As a safety measure, Metro track work spots are distinctly marked with end zones like this one in the tunnel near the Ballston Metro stop. (Katherine Frey/The Washington Post)

It has been seven weeks since Metro’s last SafeTrack surge, but the hard-earned respite is coming to an end: Surge No. 12 launched Saturday, and Northern Virginia riders will suffer yet again, with an 18-day service shutdown between Rosslyn and Pentagon stations.

The shutdown means that the Blue Line will disappear altogether from the Metro map though Feb. 28. And riders on the Yellow, Orange and Silver lines will experience the repercussions, as throngs of displaced Blue Line riders crowd onto alternate trains.

Metro General Manager Paul J. Wiedefeld said Thursday he understands that riders in Northern Virginia may be exasperated with the weeks-long detours they have endured during the course of SafeTrack — especially when unplanned disruptions and delays still occur on the system. But he said that Metro is safer now than it was before the start of SafeTrack, even if it is difficult for riders to see.

“I can’t measure what we’ve prevented by doing this work,” Wiedefeld said. “But the reality is that if we didn’t do it, we’d be in a much worse place.”

Blue Line customers in Virginia should consider alternate travel options.

(Claritza Jimenez,Danielle Kunitz/The Washington Post)

Blue Line riders who typically board at Franconia-Springfield and Van Dorn Street stations will have access to only Yellow Line “Rush Plus” trains, which will run all day and ferry them to Pentagon station and then over the river and directly to L’Enfant Plaza. But riders should expect crowding on all Yellow Line trains between Virginia and the District.

Northern Virginia Blue Line riders who commute to Rosslyn or Foggy Bottom will have a particularly circuitous route to work. They will need to jump on the Yellow Line, swap trains at L’Enfant Plaza, and ride the Silver or Orange lines back west to reach their destination.

About 3,000 daily riders begin their trips on the southern end of the Blue Line and end in Rosslyn, Metro officials said. Initially, officials had considered running the usual barrage of bus shuttles between Pentagon, Arlington Cemetery and Rosslyn stations to mimic the shuttered portion of the Blue Line.

But they later decided that directing people to the Yellow Line was a better option: traffic in Rosslyn would slow down the buses, and changing trains inside of L’Enfant Plaza would be more comfortable than waiting for buses out in the cold at Pentagon.

Regular Yellow Line trains, along with Yellow Rush Plus trains, will operate with eight minute headways during rush hour. During off-peak midday and evening hours, there will be 12 minute headways between trains.

Trains on the Green Line will run less frequently to accommodate the extra Yellow Line trains: Wait times between Green Line trains will increase to eight minutes from six during rush hour.

After 9 p.m., all trains will operate with 20 minute headways.

The year-long Metrorail rehabilitation plan includes 15 projects that will require the longest stretches of single-tracking and station shutdowns.

On weekends, the Yellow Rush Plus trains will operate only from Franconia-Springfield to Reagan National Airport stations — also with 20-minute headways.

“The impacts are going to be felt heavily, but in a geographically focused area,” said Dennis Leach, transportation director for Arlington County. “For people who live on the Virginia end of the Blue Line — it’s going to be absolutely inconvenient, there’s no question.”

Although there will be no Metro bus shuttles connecting Pentagon and Rosslyn stations, Arlington Transit offers two buses that can help displaced riders: The ART 42 carries passengers between Ballston and Pentagon stations, stopping at Virginia Square, Clarendon, Courthouse Road and the Department of Human Services. The ART 43 runs a route between Crystal City, Rosslyn and Court House stations.

Leach said ridership on those two bus lines more than doubled during previous SafeTrack surges that affected the Virginia end of the Blue Line — and that after the surges finished, many riders continued to use the buses in addition to, or instead of, Metro. That is because they are surprisingly fast and convenient, he said.

“The ART 43 is highly reliable. You can get from Crystal City to Rosslyn in 10 minutes or less,” Leach said. “We’re really urging people to use that.”

The Metroway bus runs along Route 1 between Pentagon City and Braddock Road stations.

During this surge, Metro work crews will be replacing hundreds of wooden rail ties and thousands of fasteners, as well as installing thousands of feet of new grout pads and running rails. They also will be realigning the third rail, and fixing leaks and dim lighting inside the tunnels.

Additionally, workers will perform structural work at the Arlington Cemetery station, which is aboveground.

The Arlington Cemetery station will be shuttered. People attempting to access the cemetery by Metro will need to ride the Yellow Line to Pentagon, then jump on a shuttle bus that will deliver them to the entrance of the cemetery.

Cemetery spokesman Stephen Smith said staff members have been trying to publicize the shuttles to local residents who might visit. But most tourists to the cemetery come by car or tour bus, he said.

“We know it’s an unfortunate inconvenience for those who were planning to come during this time frame, and we know that it makes visiting here more difficult,” he said.

As for people who are attending funerals at the cemetery or visiting a friend, Smith said they usually park in a lot outside of the cemetery, or obtain a pass that allows them to drive their vehicles inside the cemetery gates.

“As much as we love people coming to visit, our primary function is an act of being a cemetery,” Smith said. “So even though it’s obviously not ideal, it doesn’t really affect us that much.”

The temporary shutdown of the Blue Line will affect the rest of the system. For example, fewer Green Line trains will be available because of the extra Yellow Line trains added to serve Franconia-Springfield and Van Dorn Street stations.

But there might be fewer delays on the Silver and Orange lines, Metro spokesman Dan Stessel said, because there will be fewer trains crowding the oversubscribed Rosslyn tunnel while the Blue Line takes a hiatus.

Metro staff members will be monitoring ridership, he added, and can add more Orange and Silver line trains if crowding becomes a problem.

After this surge, one more long-term disruption is scheduled for Northern Virginia: Surge No. 13, a 37-day stretch in March and April when single-tracking will roll in phases on the southern end of the Yellow and Blue lines, between Braddock Road and Huntington stations.

After that, the 14th, 15th and 16th surges target the Green, Orange and Red lines.

Wiedefeld acknowledged that, even after the end of SafeTrack, the Blue Line will need more preventive maintenance and investment — particularly to address the capacity issues of the Rosslyn tunnel, where Orange, Silver and Blue line trains often experience delays because of backups. But for now, he said, he is simply trying to fix the most basic — and the most widespread — track defects that impede reliability.

“Let’s get that all behind us first,” Wiedefeld said, “and then we’ll talk more about the longer-term issues that we have to deal with on the Blue Line and the tunnel access issues.”