Mexico City's Metro Line 1 is the pink line. It's the first line to have opened in Mexico City, and in the entire country. This momentous event took place in 1969.
With 20 stations, the line runs for 18.83 kilometers. The 16.65 kilometers of passenger track are entirely underground. Only that bit of service track after the Observatorio station is at surface level.
Needless to say, it's a super busy Metro line. Weekends, thousands will head to Chapultepec Park. And during the week, transfer stations, and seemingly all those in the City center are going to see strong rush hours.