世界十一大地鐵系統 4. Madrid, Spain

4. Madrid, SpainThe Madrid Metro is the second largest underground system in Europe and the sixth largest system in the world. It has 141.7 miles of track and an additional 27.5 miles are expected to be completed by the end of this year. The Madrid Metro is the densest metro network in the world. Highlights: Very clean and is implementing an ecologic cleaning system. Fast rides. Affordable fares. Great progress in system expansion (47 miles of new subway lines were built between 1999 and 2003). Modern stations.