Massachusetts Bay Transportation Authority
The subway runs mostly in Boston and in the towns next to it.  There are five different subway lines, which are color-coded.  Each line runs to a different part of the city.  There are a total of 66 different subway routes in the Boston area.  The lines cross each other at different points throughout the city so people can switch lines when they need to.  A person does not have to pay to switch from one underground subway to another.