The Jubilee line is a London Underground line. Having opened in 1979 (though some sections of track date back to 1932), it is the newest line on the network. It was built in two major sections—initially to Charing Cross tube station in central London; then expanded in 1999 with the Jubilee Line Extension to Stratford station in east London. The later stations are larger and have special safety features, both aspects being attempts to future-proof the line. Following its extension into East London, serving areas once poorly connected to the Underground, the line has seen a huge growth in passenger numbers and is currently the third busiest on the network with over 213 million passengers per year. Thirteen of the 27 stations served are below ground.