Green Line derailment Near Lechmere 30 Sept 2024

Surprised that nothing was posted about this yet.

https://www.wcvb.com/article/crews-resp ... e/62475241

An investigation is underway following the latest derailment of an MBTA Green Line trolley in Cambridge on Monday evening.

MBTA officials tell Newscenter5 that the NTSB is stepping in and taking over the investigation into the derailment that sent several passengers to the hospital with minor injuries. The MBTA said that they must halt all repairs and investigation until the federal investigators arrive.

"NTSB is sending a team to investigate Tuesday’s derailment involving a MBTA light rail passenger train near Somerville, Massachusetts. Team expected to arrive tonight and tomorrow morning," the NTSB said in a statement.

Shuttle bus service is replacing train service between North Station to Union Square and the Medford/Tufts station and is expected to continue until the end of service on Tuesday.

During a press conference outside of the Lechmere MBTA station, MBTA Chief Operating Officer Ryan Coholan said that the preliminary investigation has ruled out any issues with the track structure, and that the investigation is focusing on the human factors involved with the derailment.

That derailment was on Tuesday, Oct 1. The news story incorrectly stated Monday in the first line.

From a conversation we had in the Miles in Transit discord, it seemed like the switch was set adversely since the switch prioritizes Medford trains, but didn't detect the Union train in time (maybe because it was going too fast) and the switch was changed as the train was running over it.

Operator is to verify switch is set correctly and correct signal aspect before proceeding. Any discrepancies would need to notify dispatch for instructions. Should not proceed if signal is double red.

I was thinking the switch must have been set correctly as the lead car appears to have stayed on the Union track, but a later truck split the switch?

Green Line has no automatic stop to prevent going past a red signal. It was a Union train, the first car front truck incorrectly followed the Medford route and the remaining trucks went the correct way to Union. Union goes to the right and crosses under the Medford branch.

BandA wrote: ↑Wed Oct 02, 2024 4:08 pm so there is no "positive train control", the motorman needs to follow the signal, there is nothing automated preventing them from blowing through signals?

The GLTPS (Green Line Train Protection System) is ongoing and is supposed to prevent these kinds of issues.

https://www.mbta.com/projects/green-lin ... ion-system

The previous PTC project has been deleted and new request for proposals was issued this summer. Proposals were to be received by August 27, 2024.

typesix wrote: ↑Wed Oct 02, 2024 4:24 pm Green Line has no automatic stop to prevent going past a red signal. It was a Union train, the first car front truck incorrectly followed the Medford route and the remaining trucks went the correct way to Union. Union goes to the right and crosses under the Medford branch.

I thought from the aerial shots that the front truck followed the Union route? Isn't the Union track on the left (straight) at that switch, with Medford diverging to the right?

Looking west, Union track is on the right, Medford on left. Union then curves to right before curving left and under the Medford line. Still looking west and going inbound, Union is on the left and Medford is on the right. This was done to avoid a Copley or Beacon junction, where the lines cross each other directly.

Looks to me that the train proceeded too far after splitting the switch for the situation not to include human error.

I haven't ridden this part of the Green Line yet, but does this switch not have a double red signal just preceding that demands a full stop where the operator can read the switch first? Then see that the train was going the wrong way within ten feet? Or was the line built to rapid transit standards including such double red indication clearing in the absence of other train movements to a proceed indication in advance? In which case allowable train speed across the switch might be in excess of 15 miles per hour?

The GLX still has double reds at the route switches like the subway. Operator should approach the double red slowly and wait for it to change to route indication and that the switch is set properly, before proceeding . Not allowed to proceed past double red unless directed by an inspector.

typesix wrote: ↑Thu Oct 03, 2024 6:56 pm Looking west, Union track is on the right, Medford on left. Union then curves to right before curving left and under the Medford line. Still looking west and going inbound, Union is on the left and Medford is on the right. This was done to avoid a Copley or Beacon junction, where the lines cross each other directly.

Ah, thanks...I haven't had the chance to ride it since it opened, but saw a lot of the construction from the Fitchburg...and I mixed up which line did the flyovers, etc.