Will have a 4 hour layover, is this a viable place to visit? Any other recommendations? How is traffic? Will be a Thursday afternoon/evening.

It's a great place to visit.It is very scenic You'll have to take the silver line bus from the airport into Boston.

I agree with Melissa. With only 4 hours I would recommend a short tour in Boston Common only and maybe a short walk afterward to Faneuil Hall/North End to visit food market/bar, not to mention going back to the airport is easier from there.

If you only have 4 hours, then I recommend taking a taxi or Uber from the airport so you don't lose time with public transportation, which can often be slow. The Boston Common is great; however, I would pair it with a walk around Beacon Hill or the North End. The Boston Common itself is just a wide-open park with a lot of historical value but I wouldn't say a visit to only that would be worth a trip from the airport. Hope that helps!

Sometime very busy