The Worcester intermodal yard can be seen from the Worcester MBTA/Amtrak station. They have trailer lifts and several tracks, so you should be able to see some action there. I'm not sure what hours the yard operates, but they should be open Saturday mornings if my memory serves me correctly.

The Boston rail ramp is located at the Allston/Brighton exit off the Masspike. I think this is exit 18, but I'm not sure. Anyways, you can see the yard from the highway as you take the left-hand exit. You should be able to see the action from the Doubletree hotel parking lot that overlooks the ramp. I've never tried doing this, but you might want to check it out.

Lastly, there is a third intermodal ramp and rail yard in Ayer, MA that I have never been to. Try looking for this on Mapquest.. I've heard that many railfans like this location.

I live in Brighton, and I'm telling you about this stuff off the top of my head.. I dont have a map in front of me, unfortunately. I can try and find more information on these if you're still interested.