There are two places where the median is wooded between Rts 133 and 38 along Rt 495 in Tewksbury. Near the southern tip of each bit of woodland, there is a rock-on-rock. I mentioned this earlier [Click here]
Here is a view from the south of the northern piece of median woodland.
Aside from it being amusing to hunt for rock piles while commuting, what does it mean to spot a second rock-on-rock in the 495 median strip? I think it only means that there were sites at these locations. It also means that the woods on either side of the highway are worth exploring, and so is the median itself if you could figure out how to get there. As you can see, this is something called the "Great Swamp" in Tewksbury.
CORRECTION: I was wrong, there is only one wooded median strip and both rock-on-rocks occur at its southern tip. There is a little bit of a diagonal stone wall in there, one feature is on one side of the wall, the other on the other. The "southern" outline in the map fragment above was bogus and does not exist. The "northern" one is correct.