The older of these lines is the Tünel. This line is the oldest underground metro line in continental Europe, and the second in the world after London. The Tünel is 573 m long with an altitude difference of 60 m and no intermediate stations between Karaköy and Tünel Square. It has been continuously in service since 1875. It was originally steam-powered with two wooden trains serving parallel tracks. It was modernized in 1971. Today the line is single-track with a passing loop, electrically powered and runs on rubber tyres with rebuilt ex-RATP MP 55 vehicles. A trip takes approximately 1.5 minutes. About 15,000 people use the line each day.