Metro crews work on SafeTrack stage 5 repairs on the tracks of the outbound Orange and Silver lines in Ballston. The behind-the-scenes tour of the project offered a view of its complexities — and logistical challenges. (Katherine Frey/The Washington Post)

We emerge from the subway tunnel into a sauna of heat, dust and diesel fumes. On this portion of track, between the East Falls Church and Ballston stations and flanked on either side by highway traffic, dozens of Metro track workers are hammering away, fastening bolts and revving heavy machinery as part of Metro’s SafeTrack rebuilding program.

The heat index in Ballston is pushing 100 degrees.

Reporters gathered here Friday as Metro officials showed the kinds of repairs that have inconvenienced riders since early last month.

Their goals for this fifth round of SafeTrack, on the Orange and Silver lines: replace thousands of wooden rail ties and fasteners, repair and replace the grout pads that secure the running rail, clear out the buildup in drainage systems, and finish it all in a limited window of time.

The behind-the-scenes tour of SafeTrack work offered a view on the complexities of the process — and the logistical challenges faced during the coming weeks and months.

Metro workers repair the rails for the outbound Orange and Silver lines in Ballston. (Katherine Frey/The Washington Post)

[SafeTrack closures: These D.C. Metro lines and stations will be disrupted in the next year]

Standing on a rocky section of track a few hundred feet outside the entrance to the tunnel, Metro General Manager Paul J. Wiedefeld pointed out a worn, soot-covered insulator supporting the electrified third rail. Insulators in such condition have been known to generate heat and create smoke, leading to long service disruptions and even tunnel fires.

“It just reinforces that I know we did the right thing” in launching the year-long schedule of repairs, he said, squinting against the blaring sun. “We can ignore this, we can let this go on and on and on and come out here in a two-hour window in the middle of the night and try to fix these things — we’re not going to get there.”

But even as Metro seeks to make improvements, there have been hitches. Recently, the Federal Transit Administration cited Metro for more than 100 safety defects, ranging from minor issues to serious problems, that were found during inspections of the work performed in the first two safety “surges.” The FTA’s criticisms included inconsistencies in following track maintenance standards and a lack of procedures to keep metal debris away from the third rail.

[FTA report outlines 109 safety defects]

Wiedefeld said he takes those criticisms seriously. But, he said, the normal challenges of adhering to safety regulations can be magnified when the work zone spans more than a mile, with different groups performing different kinds of work all at once.

“It’s a problem. I would love it to be zero,” Wiedefeld said of the 109 defects. “The level of work that we’re doing, the overall volume of it and then under some of the conditions you’ve seen, I think we’ve done fairly well.”

Workers are contending not only with the heat but also with the need to be cognizant of trains rushing past every few minutes on the adjacent track. Each time a train approaches, work crews need to pause. Track workers wear reflective vests, hard hats and protective goggles. They carry flashlights to navigate the tunnels and signal their presence to train operators. While walking the tracks, they aren’t allowed to use cellphones.

The grueling, round-the-clock work is done in 12-hour shifts. Managers overseeing the rebuilding program are logging something like 25,000 steps a day — just short of a half-marathon, Metro SafeTrack director Laura Mason said.

[Metro returns to Orange and Silver for SafeTrack Surge No. 5 ]

On paper, the process is laid out in extreme detail, with a precise schedule for which type of work will occur where and when during each of the 24 shifts planned for this surge. To the uninitiated, the schedule looks like a labyrinth of zigzags and multicolored lines shooting off in different directions.

The whole operation is loud, complex, risky and tiring — and it’s made a lot more challenging by the extreme heat along the tracks. By mid-Friday, empty plastic water bottles had piled up at the side of the tracks, and Wiedefeld was reminding staff members to make sure they took frequent breaks to stay alert.

The heat also adds extra work: Andrew Off, deputy general manager, pointed out a spot on the tracks where the steel was slightly warped in one direction and then another: It was a heat kink, in which the steel rails expand under the blazing sun and start to buckle. It’s a defect that would ordinarily shut down the tracks to prevent a derailment.

It was just a small crimp, almost imperceptible if you weren’t trained to look for it. Before the end of this bout of SafeTrack, track workers would need to cut out a small section of the rail and weld it back together. Another item to add to their long list of things to do.

[Heavier traffic on some area roadways as Metro’s SafeTrack is underway]

Elsewhere on the tracks, Off points out a splintered wooden rail tie that needs replacing. On outdoor portions of the system, these heavy slabs of wood secure the metal rails.

The work crews use a process that functions like a moving assembly line. First, a heavy piece of machinery rumbles in and uses a long claw to pull the tie loose. Then another machine, known as a tie shear, crushes the beam so it is easier to remove. A third machine extracts the tie.

Later, track workers bore a ditch into the gravel and slip a new tie into the track bed.

The assembly-line process makes clear why the hyper-detailed schedule is necessary.

With a long line of machines running back and forth along a single segment of the tracks, work crews need to ensure that no other groups will get in their way — and, for example, try to start replacing fasteners while rail tie machinery needs to move over the same stretch.

A deviation from the schedule, such as an unexpected need for a particular type of machine, would disrupt the whole process.

Different types of heavy equipment and large items, such as wooden ties and steel rails, can be transported only on tracks, and all those items need to be carried out in a particular order so that one important piece of equipment isn’t stuck on the wrong side of a zone on the tracks where work is already in progress.

It’s a surprisingly complex process.

As the machines whirled into motion, drivers coasting west on Interstate 66 tooted their horns — in support, or indignation, or maybe just wanting to see if they could get attention. And up on an overpass, a man in a T-shirt and cargo shorts stood transfixed, getting an aerial view of the work that will continue for another week.