Just like New York City, the rail transportation system in São Paulo is already big and continues to grow! Six train lines connect to five subway and a monorail line. Currently, another monorail is under construction and plans exist for two more lines.
São Paulo has some of the worst traffic of any city. I've sat in traffic at midnight on a weekday. It is so bad that buses, too, will get stuck, often doubling my commute time. Because of this, it is often fastest to use the metro or train lines to get around the city.
I am from Minneapolis which only has two light rail lines and one commuter train. Being able to take the subway to almost all the places I need to go in São Paulo feels exciting. I am always in awe about the amount of planning and maintenance that goes into the massive infrastructure of the stations (sometimes you have to take seven escalators to get to the platform). The mainline that I take, Line 4 Yellow, is the first fully automated subway line in Latin America and was the first public-private transportation project in São Paulo. That means that a private company built and operates the line, but it connects with the public lines and as a commuter, you pay the same fare.