The Underground has its origins in the Metropolitan Railway, the world's first underground passenger railway. Opened in January 1863, it is now part of the Circle, Hammersmith & City and Metropolitan lines; the first line to operate underground electric traction trains, the City & South London Railway in 1890, is now part of the Northern line. The network has expanded to 11 lines, and in 2016–17 carried 1. 379 billion passengers, making it the world's 11th busiest metro system. The 11 lines collectively handle approximately 4. 8 million passengers a day.