Passengers using one of many escalators at L'Enfant Plaza Metro station in Washington, on Feb. 9, 2016. (Linda Davidson/The Washington Post)

Metro Blue Line riders relieved to see their trains back in service after 18 days of SafeTrack repairs last month: Don’t get too comfortable. Ditto for those who switched to the Yellow Line to get through the last surge.

SafeTrack rumbles back through Northern Virginia for the final time this month, with 36 days of round-the-clock single-tracking, causing slowdowns and headaches in the city of Alexandria and Arlington and Fairfax counties — and potentially snarling commutes in other parts of the system. This time around, the track work, which started Saturday, will be performed in two phases: the first on the Blue and Yellow lines through April 1, and then shifting exclusively to the Yellow Line, April 2-9.

The initial work zone stretches from the Braddock Road station to the Van Dorn Street station on the Blue Line and to the Huntington station on the Yellow Line. For that phase, Yellow Line trains will run every 24 minutes from Huntington to Mount Vernon Square — even during rush hours — and Blue Line trains will run at that same frequency systemwide, including rush hours. Yellow Line Rush Plus service, which normally provides Blue Line passengers an alternative route to the District, will be halted. Though service will be more frequent from Reagan National Airport northward, riders on both lines are being urged to seek alternatives.

“What appears to be at first blush a fairly localized impact has reverberations all throughout the system,” said Metro board member Christian Dorsey, who represents Arlington. “Looking at alternatives will be essential to get you from where you are to where you need to be with a minimum of disruption and a minimum of frustration.”

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

South of National Airport, service will be skeletal, with a fourth as many trains as normal through April 1. For riders north of the airport, it won’t be smooth sailing either. Half the usual number of trains will serve stations up to Rosslyn and L’Enfant Plaza. With those levels of service, any unexpected disruption could cause widespread crowding and delays. Metro says it is staging additional employees and trains within the system in case of a breakdown.

Officials, meanwhile, urged riders to stay away from the work zone if possible.

“I want to reiterate the importance of using alternate modes of transportation during this period of time so that we make sure that we are freeing up space on our roads as well as allowing for repairs to be made to our Metro system,” said Sharon Bulova (D), chair of the Fairfax County Board of Supervisors.

With the latest surge, however, there’s a silver lining: If all goes to plan, it will be Virginia’s last taste of the year-long repair program, which has disrupted travel across the region and driven riders away from Metro at historic rates, causing the agency financial distress.

“For those riders in Virginia who have long experienced issues on the Blue Line, whether it’s reduced service, unreliable service and then, the previous surge and the current surge, I have a message,” said Dorsey. “The light is at the end of the tunnel. We’re almost done. April 9 we should get something more closely resembling the service that we want to provide on a regular basis.”

For Blue Line riders, who have been dealt their fair share of SafeTrack-related pain, relief will come soonest, with repairs concluding on April Fools’ Day — perhaps an unfortunate omen.

After the first round of repairs concludes April 1, track work will shift exclusively to the Yellow Line while the Blue Line returns to its normal 12-minute waits. Round-the-clock single-tracking will take place between the King St.-Old Town and Huntington stations, keeping slowdowns in place, including during rush hour. Like before, trains from Huntington to Mount Vernon Square will run every 24 minutes, with additional service from National Airport to downtown.

In all, the surge is expected to affect 43,000 trips each weekday. At a news conference on the repairs, officials urged riders to find different ways of getting to and from work over the next month.

“Please rethink your commute and try alternate travel options such as walking, biking, using our DASH bus system or Metrobus, carpooling or using Amtrak, [Virginia Railway Express] or telecommuting,” said Alexandria Mayor Allison Silberberg (D).

Free shuttle buses will ferry passengers between the Franconia-Springfield and Pentagon stations. Alternative bus routes include the 10A, from Alexandria to Pentagon, the 11Y, from Mount Vernon to downtown Washington, and Metroway, the bus rapid transit service from Braddock Road to the Pentagon City Metro station. VRE is another option: Officials recommend the Fredericksburg Line for an alternative between Franconia-Springfield, King St.-Old Town or Crystal City, and the District. Fairfax Connector Route 394 will run more frequent service from the Saratoga Park-and-Ride to the Pentagon.

Capital Bikeshare, which enacted a $2 single trip fare for SafeTrack, was pitched as another option. And slugging, the informal carpooling system popular in Northern Virginia, was hailed as yet another.

Metro General Manager Paul J. Wiedefeld pointed out that Surge 13 is expected to be the last with significant impact across the system.

“The good news is this is our last major one,” Wiedefeld said. “The remaining tend to be at the end of the system so they don’t have a major impact on service.”

Surges 14 and 15 encompass repair work on the Green and Orange lines, the first stretching from the College Park station to the Greenbelt station beginning in mid-April and the latter from the Minnesota Avenue station to the New Carrollton station later on. A subsequent surge is planned for the Red Line from Twinbrook to Shady Grove.

The program is expected to conclude in June.

Wiedefeld lauded the program’s progress over eight months of repairs, despite the impact on ridership.

“We’ve achieved quite a bit,” he said, pointing out that 53 miles of track have been covered, representing 23 percent of the system. “If you just think of the crossties and the fastening system that holds the rail down we’ve done the equivalent of the Silver Line extension.”

Bulova urged patience as the system continues to undergo much-needed rehabilitation.

“Please help with this process in letting our employees use telework and flexible time so that we are giving people the ability to be off the roads during peak hour,” she said.

The surge is just the latest test for users of the beleaguered system and the region’s transportation network. But Metro Board member Cathy Hudgins, who represents Fairfax County, said it’s manageable if riders take the appropriate precautions.

“Don’t just hop in your car,” she said. “Plan your ride, decide where you need to go, when you need to get there, and I think we’ll get through this one as well.”