Boston September 16, 2019 6:20 pm MBTA Says Broken Axle Caused Red Line Derailment Following an extensive investigation, MBTA officials now say a broken axle is to blame for a derailment on the Red Line back in June. US & World Videos 1:29 Sumner Tunnel in Boston to close for one month 2:03 Mass. school officials threaten to suspend student protesters 2:13 Karen Read trial Day 6: Witness testimony resumes 6:03 Tensions rise during campus protests at MIT and Harvard 20:19 Karen Read's attorney accuses witness of perjury at murder trial