I think the answer is that there is relatively little rail activity at iron horse park. Check google maps. Most of the real estate is not rail oriented anymore
Funny you should say that because I left my appointment in Westwood and drove to North Billerica thinking I'll catch SOMETHING there.
I get off 495 and theres a freight train going under the bridge. I beat it to North Billerica and there was a commuter rail train pulling in as I pulled up. So I missed filming that but I immediately caught the freight! 17 cars too, bigger than anything that passes through woburn these days. I guess I was just lucky. I wish I were a minute or two earlier so I could have filmed them both. This station is very well lit, great for after sunset filming!
https://www.youtube.com/watch?v=Ur-Xzg3pbWE