The problems have been getting worse. Cracks on Metro's 106-mile rail system have become more frequent in the past three years, according to transit agency statistics. Last year, Metro had 49 cracks on the system compared with 33 in 2010, and 19 in 2009.
"In part, this is reflective of aging infrastructure and is exactly the reason we're doing so much track work to restore the system," Metro spokesman Dan Stessel told The Washington Examiner.
|Metro's cracked rails|
In January, the agency had six cracked rails, five of them that caused delays.
The agency had six incidents last January, too, Stessel said, and cracking may follow seasonal patterns.
It is not clear what caused the recent cracks, though.
Steep temperature jumps can cause the metal to expand and contract, which can fracture the rail immediately or cause longer-term stress. Water corroding the tracks can make matters worse.
If the track bed or the rails themselves aren't even and aligned, the pressure of trains passing through also can stress the metal rails.
But Stessel also said the agency may be better at finding the fissures, with higher standards and better technology than in the past.
The agency relies on people, known as trackwalkers, and ultrasonic equipment to spot the breaks. Crews inspect the rails twice a week, but now do it more often in areas with the oldest rails, he said.
This summer, the agency will be getting a new piece of equipment called a track geometry vehicle that uses thermal imaging and lasers to give a better picture of the tracks. It's the difference between an X-ray and a three-dimensional magnetic resonance imaging, Stessel said.
The agency also plans to run the machine monthly to pinpoint trouble spots before cracks occur, instead of the quarterly ultrasonic tests it does currently.
Cracks aren't the only rail defects that can waylay Metrorail trains. The metal rails can chip, as one did Monday. They can pop out of their footings in what is called a heat kink.
But cracks are the most frequent rail defect to slow trains, becoming so common that regular riders have added it to their Metro lexicon along with "single-tracking" and "off-loaded train."
The cracks can cause bigger problems, though. A 2003 derailment on the London Underground was blamed on a cracked rail.