Mbta commuter rail is not a good system. I tried it for a month (Fitchburg line), the train was scheduled once an hour and was regularly half an hour or more late. The passes were exorbitantly expensive, too; more than the cost of car ownership for the same route. I so badly want it to work, I love the idea of it, but the day to day experience is comically bad.
I checked Wiki for more info about the MBTA Fitchburg line. I don't know from what station you rode, but MBTA commuter fares are much cheaper than the total cost of ownership of a car per mile. Estimates are about 81 cents per mile to drive a car (depreciation, fuel, maintenance, repairs, insurance, etc.) -- I Googled for it. Fitchburg station to North station is 53.7 miles, which would cost 43.50 USD to drive a car. The current MBTA fare is 12.25 USD -- much cheaper than owning a car.