[1] https://www.boston.gov/news/new-steps-reduce-vehicle-emissio...
They are free on only 3 lines (plus SL1 leaving the airport) https://www.boston.gov/news/mayor-wu-takes-steps-expand-fare...
So it's not as simple as take the bus. (Which doesn't exist.) But that's fine. I mostly just don't go in.
The bike lanes mentioned above all, by physical necessity, come at the expense of cars, either by reducing parking lanes or reducing driving lanes. Even if there were the same amount of traffic, fewer cars would be on the road because there is less road to be on.
Not even the best transit cities have transit every 5 minutes all over the city. There is a lot of room to improve in them all
The easiest way to do that is reduce commuting trips, as those are very common, but you can reduce trips in other ways, such as allowing more gas stations/convenience stores. If it's a five minute drive to the grocery store but a two minute walk to a 7-11, some of those trips to the grocery store will be replaced with walks to the 7-11.