The longest phase of the Washington Metro’s 10-month maintenance overhaul is on schedule to begin Thursday, marking the start of 42 days of continuous single tracking on the western edge of the Orange line, the agency said Monday.

The ninth out of the 15 phases of the SafeTrack program, as Metro has dubbed its maintenance effort, will affect service between the West Falls Church station and the Orange Line’s end at the Vienna station. In a departure from previous phases, the Washington Metropolitan Area Transit Authority, as Metro is formally known, will run a “shuttle train” during the project. Officials said they hope the shuttle train will help keep the rest of the line running smoothly while work is going on.

​Until late October, riders heading downtown will board the shuttle train at Vienna and exit at West Falls Church, then board a regular eastbound train and continue their trip. The shuttle train is possible because of a third track in the area that is not common in other parts of the system, Metro General Manager Paul Wiedefeld said.

The process would work the same way in the other direction. Trains will run about every 24 minutes during the project, compared to the usual pace of every six minutes, according to Metro. In addition to the shuttle train, Metro will operate an express bus between Vienna and West Falls Church.

In addition to the weekday single-tracking during the project, the affected portion will shut down completely during four of the weekends. Metro announced that move – which wasn’t part of the original SafeTrack plan – last month in an effort to further concentrate on problems that were discovered after SafeTrack work began in June.

Wiedefeld said changes to the final five phases of the program would be announced in roughly the next week.

The latest phase comes after the Federal Transit Administration issued three reports in recent weeks criticizing the condition of Metro’s rail system. Lawmakers, including Virginia Reps. Gerald E. Connolly, a Democrat, and Barbara Comstock, a Republican, have also raised concerns about the system’s inconsistent performance.