MBTA management today released the results of their investigation of the causes of the Red Line derailment in June.

They have concluded that the car derailed because its axle failed. The axle failed because it had been damaged by arcing electrical currents. Normally, direct current runs from the third rail through the motor back to ground through the axle and the wheels. The electrical arcing was caused by deterioration of a ring that normally conveys current from the motor to the rotating axle. Overtime, the arcing hardened the steel of the axle and made it brittle.

The attached presentation explains the issue in more depth and also shows that service is approaching very close to its pre-derailment levels. Delays still persist between North Quincy and JFK/UMass. In this stretch signal replacement work is still in progress with completion hoped for next month.

In the presentation, the Deputy General Manager explains that the impending axle failure would have been detected by the regular ultrasonic inspection of axles which occurs every two years. To reduce risk, the T has done a reinspection of all the axles in this type of car and will do so every one year. Additionally, during their 8500 mile inspection (roughly quarterly), engineers will conduct a full inspection to the current ring and take out of service any rings that show material deterioration.

To see some of the questions and answers from the MBTA Board Meeting, you can view the proceedings starting at approximately 2.5 hours in the livestream at this link. Questions will continue as to how this particular ring got so badly damaged. A State House News reported that the Deputy General Manager said:

How exactly the ring came to be so corroded remains unclear . . . A December 2018 preventative maintenance inspection, one conducted roughly every three months, noted that the assembly itself was missing the cover that keeps it sealed. . . . . there are no other immediate risks to the system from similar causes. Crews performed ultrasonic inspections on the entire Red Line fleet after the derailment and pulled seven axles flagged for potential issues from service, and two ground rings that demonstrated even the start of damage were also replaced.

For previous updates, please see this link.

Published by Will Brownsberger

Will Brownsberger is State Senator from the Second Suffolk and Middlesex District.

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12 Comments

  1. I had read the very brief description from a Boston Globe summary and couldn’t understand the connection between electrical conductivity and the axle failure. This description makes more sense (from my limited electrical engineering perspective). Thank you.

  2. Thanks Will,

    This is so clear and also seems to illustrate the necessity of fully funded repair and/or replacement of a nerve- wracking, loud, dirty system of cars and “catch up” approach to maintenance and operation.

  3. Dear State Senator Brownsberger,

    Thank you for keeping us updated. I hope regular maintenance will be done to prevent further deterioration of the T. I also hope more resources can be directed to improving reliability and service. You have been fighting the good fight for funding, keep up the good work.

  4. Thanks for updating. This confirms that the current system is aging (out dated). Can we speed up the unnecessary delays of putting new cars into red- orange lines? Why would it take 8 to 10 years to qualify a subway car that has been put into use for quite some years in another country? Why would it take them ( MBTA ) so long? What will happen next time an aging subway car fails?

    Thanks for your patience.

  5. Thank you, Will, for providing the technical details! So many news reports these days don’t tell me enough. I took me awhile to find out that the reason service has taken so long to restore was that three cabinets of critical signal equipment were destroyed in the resulting crash, if I’m not mistaken. We keep saying how important STEM is in education, then leave the public in the dark about these things.

  6. Why are our elected officials not calling out Gov Baker? Seems like he’s getting a pass. There have been way too many of these types of issues on the T. All he does is ask for more money from rider’s and in return we get a terrible product. In 2015 he was all over Beverly Scott for the bad performance of crumbling transit system and it’s only got worse under his watch. I watched a T official day this one was on them. They’re all on them.

    1. I think we all bear responsibility for the condition of the T. The current conditions reflect decades of under-investment in equipment. Responsibility for under-investment falls on many past and present officials, and, to be fair, on voters who have voted to cut taxes. But for a series of tax cut ballot questions in the 90s and more recently, we would have about $3 billion more annually to spend on all state needs. When agencies feel a budget squeeze, all too often they skimp on maintenance and equipment replacement.

      At this point, though, I believe both the legislature and the Governor are all about giving the MBTA the capital funds it needs and the MBTA is spending money as fast as it can to fix the conditions.

  7. The thing that struck me about this report is that somebody found that a cover was missing — and apparently did nothing to check whether anything the cover should have protected was damaged. That could have been that the person who found the problem wasn’t trained to check further, or that somebody up the line said it couldn’t be a problem; in either case there’s a management issue that I hope somebody is looking at.

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