Metro Line M4 (Budapest Metro) Metro Line M4 (Budapest Metro) Line 4 (officially: South Buda–Rákospalota (DBR) Line, Metro 4 or M4, and unofficially: Green Line), is the fourth line of the Budapest Metro. It opened on 28 March 2014. The first section, 7.4 km in length and consisting of ten stations, connects the southwestern Kelenföld vasútállomás located in Buda, and the eastern Keleti pályaudvar in Pest, under the River Danube. While three additional sections — one an eastern extension to Bosnyák tér, the second west to Virágpiac, and a third further east to Újpalota — have been planned, these remain unfunded by the Budapest city
Budapest a long island south from Budapest. District XXII is still on the same route in southwest Buda, and finally District XXIII is again in southernmost Pest, irregular only because it was part of District XX until 1994. Budapest is the most populous city in Hungary and one of the largest cities in the European Union, with a growing number of inhabitants, estimated at 1,742,000 in 2014, whereby inward migration exceeds outward migration. These trends are also seen throughout the Budapest metropolitan area, which is home to 3.3 million people. This amounts to about 34% of Hungary's population. In 2014, the