Which subway line primarily serves the Upper East Side of Manhattan?

The Q train primarily serves the Upper East Side of Manhattan, particularly since it underwent an extension to reach this area more directly. Running from Astoria in Queens to Coney Island in Brooklyn, the Q line includes stops at key locations along the Upper East Side, such as 72nd Street and 86th Street, making it a convenient option for residents and visitors traveling in this part of Manhattan.

This focus on the Upper East Side is particularly significant when considering the Q train's operation as one of the newer lines with modern features, catering to the diverse crowd that utilizes transportation in this affluent neighborhood. The other train lines mentioned may serve adjacent areas but do not have the same level of direct service to the Upper East Side.