Days after a BART rail between Civic Center and 16th Street stations suffered a massive split that snarled the commute for an entire day, BART officials still aren't sure why the tracks fell apart — and admitted that, despite repeated assertions that this is the kind of thing that happens when your system is 42-years-old, the trackway that disintegrated had only been there for four years.

You remember Wednesday! A train operator noticed that the stretch felt "rough" as he or she passed through at 9:20 that morning, and called it in to HQ. It took until 4 p.m. to fix the track, which had a break that looked like this:

Even then, "trains could not run over the section at full speed and delays persisted," KTVU reports. BART crews did a final round of fixes overnight, and trains were back to running on it at normal speeds by Thursday morning, Trost says.

During the crisis, officials for the transit agency alluded to BART's aging, damaged trackways and their need for a jaw-dropping $9.6 billion in improvements with a bit of a ¯\_(ツ)_/¯ ...see this is what happens, y'all.

However, late yesterday Trost said in a statement that the piece of trackway that caused all the issues was a fairly new one, replaced in early 2011. According to BART, most pieces of railway should last around 25 years.

So why'd this comparatively fresh and new piece of BART track fall apart, while pieces ten times its age are doing just fine?

The jury's out on that one, Trost says, and will remain out until the broken piece returns from "lab testing."

“It concerns me and that's why the BART staff has sent [the piece] out for analysis so we know what we're dealing with instead of shooting in the dark,” BART Board President Thomas Blalock told KTVU.

Though no one is sure how long it'll take the lab to get us an answer, BART's board members say they expect a report on the snafu at their next meeting on May 14.

Meanwhile, they're going full speed ahead on trying to pull together that $9.6 billion, with Trost telling KCBS that "Luckily, BART has identified funding for half of that."

“It leaves our unfunded need at $4.6 billion. And that’s not even really to expand the system, that’s to take care of the current system.”

Previously: 'Deformity' Causes Major BART Delays Throughout San Francisco
BART's Track Maintenance Problems Way Bigger Than Previously Reported