The City of Cambridge doesn't seem to know what to do about this; nor do they apparently care enough to take an active role in resolving this. I was told on the phone that if the train were blocking a road, it would be a police matter. The train, tracks and crossing are owned by CSX. Several people have reported the issue to CSX already. The train is still there, 24 hours later. I guess until someone moves it I will keep watching people clambering over the train from my office window.

Those tracks are owned by the state transportation department, MassDOT: http://www.massdot.state.ma.us/Transit/

You're right, sorry. We have reported this issue to both MassDOT (tracks and crossing) and CSX (train). It doesn't look like either really cares enough to do anything about it, though.

Hey, it could even turn out that the train isn't owned by CSX... really, this is outside my area of expertise. If only some more qualified person from the City could take over and call the proper people on behalf of the affected residents and commuters in Cambridge, I could go back to doing things to which I am... less unsuited.

Finding no other effective reporting mechanism, I tweeted it @massdot, and they responded that they were forwarding it to MBTA Commuter Rail, who apparently have responsibility for the tracks.

Cambridge has a Pedestrian Committee made up of resident volunteers who work at improving walking around the City. This is something they should care about:
https://www.cambridgema.gov/cdd/transportation/forthepublic/pedestriancomm

(I'm on the Transit Committee and if I thought we could help, I'd pursue it myself.)

Looks like the MBTA commuter rail folks have decoupled the train and are moving part of it so the crossing is clear! Hooray! Thanks Saul and anyone else who helped here.

Thank you for reporting this issue. While the City is not responsible for addressing issues on state property, we have shared this information with MassDOT and asked them to take action.

If you would like to follow up directly, please contact MassDOT at 877-MA-DOT-GOV.