fishing boats. The main harbour which serves Rome is Port of Civitavecchia, located about northwest of the city. The city suffers from traffic problems largely due to this radial street pattern, making it difficult for Romans to move easily from the vicinity of one of the radial roads to another without going into the historic centre or using the ring-road. These problems are not helped by the limited size of Rome's metro system when compared to other cities of similar size. In addition, Rome has only 21 taxis for every 10,000 inhabitants, far below other major European cities. Chronic congestion caused by cars during the 1970s and 1980s led to restrictions being placed on vehicle access to the inner city-centre during the hours of daylight. Areas, where these restrictions apply, are known as Limited Traffic Zones (Zona a Traffico Limitato (ZTL) in Italian). More recently, heavy night-time traffic in Trastevere, Testaccio and San Lorenzo has led to the creation of night-time ZTLs in those districts. A 3-line metro system called the Metropolitana operates in Rome. Construction on the first branch started in the 1930s. The line had been planned to quickly connect the main railway station with the newly planned E42 area in the southern suburbs, where 1942 the World Fair was supposed to be held. The event never took place because of war, but the area was later partly redesigned and renamed EUR (Esposizione Universale di Roma: Rome Universal Exhibition) in the 1950s to serve as a modern business district. The line was finally opened in 1955, and it is now the south part of the B Line. The A line opened in 1980 from Ottaviano to Anagnina stations, later extended in stages (1999–2000) to Battistini. In the 1990s, an extension of the B line was opened from Termini to Rebibbia. This underground network is generally reliable (although it may become very congested at peak times and during events, especially the A line) as it is relatively short. The A and B lines intersect at Roma Termini station. A new branch of the B line (B1) opened on 13 June 2012 after an estimated building cost of €500 million. B1 connects to line B at Piazza Bologna and has four stations over a distance of . A third line, the C line, is under construction with an estimated cost of €3 billion and will have 30 stations over a