I've long been aware of these cars here: https://www.google.com/maps/@42.2117447,-71.0006897,101m/data=!3m1!1e3 They are mostly tank cars with a few hoppers and covered hoppers. They can be seen from the upper level of the commuter Bi-Level cars in Braintree, MA. near the Red Line, (light rail), and Commuter Station. I have been unable to discern what local industry they are serving. Or? Does the MBTA use them? Just speculating, is this a MOW storage yard? I will be trying to get down thre, (without trespassing), this coming week. Based on a shadow there appears to be a tall fence which might interfere with my efforts. ThaNKS!
It is possible they are simply using those tracks to hold the cars for a nearby industry. There are maritime and other uses in the vicinity.
Looks like the best access is behind Pet Smart / Hobby Lobby. I see at least two of the tank cars with reporting mark SHQX. If you can find out what that is it may be a clue.
The hoppers are high-side gondolas used in scrap service. You can see them on Google Earth too, and they are most likely TROX-lettered for Trojan Recycling, I recognize the logo. I'm not sure on the tank cars. They had lease reporting marks on street view, but one had a 3265 corrosive hazmat placard. I think that is for organic corrosive chemicals, but I couldn't find any information on a specific product it's used for.
I followed the lines around a bit and did see what may be a liquid transload facility next to the Naval Shipbuilding Museum.