China's longest subway, stretching 50 kilometers running southwest to northwest of Beijing, will begin its trial run by the end of 2010, sources with the subway company said Wednesday.

Beijing subway

The new Line 4 will be extended 22.5 kilometers further south from the current Line 4 that ends at the South Fourth Ring Road and eleven passenger stations will be added.

The construction of the extension line has already been completed and engineers will conduct an important operational test next Monday, said officials with the Beijing MTR Corporation Limited.

The current Line 4, launched last year, is 28.2 kilometers long and has 24 stations.

Local transportation officials say the extended Line 4 will significantly ease the heavy strain on roads in the southern part of the city.

Beijing's peripheral villages and towns are undergoing rapid urbanization. Meanwhile, a growing numbers of wage-earners who choose to live in less expensive homes far from the city center have created a huge demand for fast intra-city transit.

Beijing is among the most congested cities in the world, with over 4 million private cars on the roads. However, authorities are rushing to build more subways to ease the traffic.

Beijing has prolonged transport regulations enacted during the 2008 Olympic Games to restrict road traffic by the last number of car license plates. However, any relief has been overshadowed by the fast increase of vehicles on road.

Five new subway lines, including the extension of Line 4, will open in 2010. Beijing plans to extend subways to reach 561 kilometers by 2015.