So I took that opportunity to bike up and do the first leg of the Bruce Freeman Rail Trail - it's delightful! The first phase opened just a couple weeks back, on the rainiest day we in August. (My band played at the opening too, though I must say that the quality of our playing was appropriate to the weather.)
I got onto the trail at its southern end, on Rt 225 in Carlisle at Rt 27 (Acton Rd). There were lots of people out - biking, walking, skating, etc. - just what you want to see. The quality of the paving and infrastructure are all first rate. The width of the path is a little variable, but that isn't a big deal. Seems like some of the markings aren't consistent yet, so maybe they'll work on that.
I only had time to do the first few miles, since I was meeting the family for the hike. Hart Pond was a great place to duck out - it's a beautiful spot with a little beach and a playground. From there, it was an easy jog onto Proctor Road, which turns into Old North Road after a bit, and finally turns into one of our fave trails in Great Brook Farm! That was a surprise to me - I was toddling along a nice path, and popped out right behind the interpretive center in the park.
Here's a little video from the morning.