MBTA third-rail inspections to begin tonight

MBTA inspectors will begin scrutinizing the third rails of the T’s subway tracks tonight after the end of T service in an effort to prevent future fractures similar to those responsible for widespread commuting delays this week.

Two cracks on Red Line rails — one on Tuesday night, the other Wednesday morning, both at JFK/UMass Station — prompted Beverly A. Scott, general manager of the Massachusett Bay Transportation Authority, to call for a widespread audit of the third rails on the Red, Orange, and Blue lines.

The third rail delivers electricity to the trains. The cracks are believed to have been caused by cold weather, which caused the metal to contract and fracture at the points where the rails were welded together. A crack in the rail is not dangerous — without power, trains simply come to a stop — but T officials intend to inspect the welding on third rails throughout the T system to ensure that future bouts of cold weather do not cause the same disruptions in service.

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T officials are still awaiting a formal plan that will outline the scope and prospective timeline of the inspections, but staff decided to get a jump on the endeavor.

Thursday night, they will conduct the first round of inspections.

“We’re starting this now,” MBTA spokeswoman Kelly Smith said. “We want to get it done as soon as possible.”