The London Underground metro system, often called the Tube, is the world's longest underground railway at about 400 kilometers of track. The Underground services three million people daily at 268 stations on 11 lines, including Bakerloo, Central, Circle, District, Hammersmith & City, Jubilee, Metropolitan, Northern, and Piccadilly. The Victoria and Waterloo City Lines connect the central city and many suburbs to the north of the Thames. The Underground is divided into six zones, and fares are dependent on zone and time of day, with prices ranging from GBP 2 to GBP 6 per trip. The Oyster Card, introduced in 2003, is an electronic card that covers particular zones on a weekly or monthly format.