In the midst of Wednesday’s morning commute, on the coldest morning of the year thus far, the Green Line stopped running. A cable fire in the tunnel between the Copley and Arlington stations disabled service through the heart of downtown – between Kenmore Square and Government Center – as well as service on Huntington Avenue’s E-Line. Within the same time period, three Red Line trains died on the tracks, delaying service for countless more.This is a common refrain for MBTA commuters. Not even three weeks ago on Jan. 4, the Red Line and nearly 25 percent of commuter rail trains suffered delays during the morning commute when temperatures dropped to seven degrees. This phenomenon is nothing new. Two years ago today, 63 percent of commuter trains were delayed while temperatures dipped below zero.