On October 1, 2024, about 4:46 p.m., eastbound Massachusetts Bay Transit Authority (MBTA) Green Line train 3874-3718 derailed its leading railcar at MBTA’s Red Bridge interlocking in Somerville, Massachusetts.[1] Train 3874-3718 was a light rail vehicle composed of two railcars. About 50 passengers and 2 crewmembers were on board. Less than a minute before the derailment, the train departed Lechmere Station in Cambridge, Massachusetts, and headed east along the MBTA Green Line. The train entered a 10-mph zone at 36 mph, passed through a double red signal (which requires a stop) west of the Red Bridge interlocking, and reached a switch that was still moving to direct the train into the diverging track as required by its route. When the train passed over the switch, the lead truck of its leading railcar continued straight, while the next two trucks of that same railcar took the diverging track and then derailed.[2] (See figure.) Seven passengers were transported to a local hospital with minor injuries; no other injuries were reported. Damage estimates were still being determined at the time of report publication. Visibility conditions at the time of the accident were clear. The weather was about 62°F with no precipitation.

​While on scene, National Transportation Safety Board (NTSB) investigators completed interviews; reviewed data from locomotive event recorders, the signal system, and security cameras; and inspected railroad equipment and track conditions.

The NTSB’s investigation is ongoing. Future investigative activity will focus on speed rules compliance and internal and external oversight.

Parties to the NTSB investigation include: 

• the Federal Transit Administration, 
• the Massachusetts Department of Transportation, 
• the Massachusetts Department of Public Utilities, 
• MBTA, and 
• the Boston Carmen’s Union 589.​​