There are a few buses. Depending on where in the area you are, one might be less walking and faster than the train.
- 70 or 71 from Watertown to the RL
- 57 to the GL
- 501 or 504 express buses from Newton Corner to downtown. More expensive than a standard fare but you can pay the normal way (charliecard or contactless) and it's probably the fastest.
Check out the bus system map: https://cdn.mbta.com/sites/default/files/2025-08/2025-08-25-system-map.pdf
And MBTA's trip planner (better than Google's): https://www.mbta.com/trip-planner