THE Pearl River Delta (PRD) in southern China encompasses several cities each with a population of one million or more stretching from Hong Kong via Shenzhen and Dongguan north to Guangzhou and then south down the western bank of the Pearl River through Foshan, Zhongshan and Zuhai to Macau. These cities merge into one another to form a continuous settlement area, making it by far the largest urban area in the world.

The population of the PRD more than doubled between 1991 and 2001 rising from 20 million to about 42 million. Since then the combined population has grown to around 45 million inhabitants, and it is still rising although not at the previous explosive pace.

The area is already served by a steadily expanding network of highways which is being supplemented by numerous high-speed rail lines under development as part of the 2008-2020 Pearl River Delta reform and development master plan.

With a population of 12.7 million, Guangzhou is the largest city in the PRD and is situated at the apex of the delta. The first metro line opened in 1997, but expansion of the system did not initially keep pace with the enormous growth of the city. By 2003 the first two metro lines totalling 36.8km had been completed, while another two new routes were added in 2006 in addition to extensions to the initial lines which expanded the network to 88.6km.

The staging of the Youth Olympics in 2010 was a major incentive for the city to accelerate metro construction. It was planned to expand the network to eight lines totalling 237km, but unexpected structural problems encountered during the construction of Line 6, as well as financial constraints, meant that by the end of 2010 only seven lines totalling 216.5km were in operation.

The new lines included the first cross-city line to neighbouring Foshan - the Guangfo Line - while two lines run far into the southern suburbs. Line 3 serves the new Baiyuan Airport to the north, runs entirely underground, and has a total length of 67.5km, making it the world's longest metro line. Line 3 serves the new city centre in the eastern part of Guangzhou. Due to the relatively long distances between stations, a parallel 3.9km underground peoplemover equipped by Bombardier was constructed.

The Guangzhou metro currently totals 240.8km including the 5.7km section of the Guangfo Line within the city. Further expansion is underway up to 2016 which will add another 293.5km to the network, with yet more lines to follow by 2020.

Metro construction in the PRD is no longer restricted to Guangzhou. The fishing village of Shenzhen was chosen in 1980 as the location for China's first special economic zone. The new city expanded rapidly into a 9-million-population metropolis with skyscrapers rivalling those of its southern neighbour Hong Kong. Metro construction began in December 1998, and the first two lines totalling 20.9km went into operation in December 2004.

Even before their completion, a second phase of construction was already underway with extensions to the two original lines and three additional lines. By 2011 the network had reached 170km. Investment between 2008 and June 2013 amounted to Yuan 84.9bn ($US 13.8bn).

Work is now underway on phase three which is expected to double the size of the network by 2018. The cost of phase 3 was originally estimated at Yuan 125.6 trillion, but more recent estimates put the cost at Yuan 160bn.

Land acquisition is underway for Line 6 and a ground-breaking ceremony took place in December, while the franchise model is being strengthened to allow development around the stations. Line 6 will provide an important link to the northwestern parts of the city.

Shenzhen city council decided in 2013 to build some extensions to the metro under phase 3 which is already underway, although they still have to be approved by the State Planning Commission.

This would transform phase 3 as it would expand it to 241km. The 28.8km Line 10 serving the populous Longhua district in the north is needed to relieve overcrowding on Line 4.

Shenzhen's 2007-2030 transit plan calls for the construction of a 16-line urban rail network of about 597km with 371 stations.

Pearl-RiverA separate light rail network has been under construction since the end of 2013 in Longhua district. The first two lines totalling 11.5km with 21 stations will be operated with 35m-long low-floor LRVs, and are expected to open in October. The cost of the two lines is estimated at Yuan 1.3bn. They will be the first of three planned lines totalling 51km.

Between Shenzhen and Guangzhou lies the city of Dongguan with a population of 8 million. None of the city's railways currently serve the city centre, but this deficiency will be corrected when the first phase of metro Line R2 is completed in April. Work on this Yuan 18bn project has been underway since 2010, and the 37.7km north-south line will have 20 stations, most of which will be underground. Line R2 is the first of four planned lines with a total length of 218km. Three lines totalling 126.9km are planned under the 2013-2019 expansion programme at a cost of Yuan 74.8bn. Work on the first sections of lines R1 and R3 are expected to begin this year.

East of Dongguan is Huizhou, which is now home to around 4 million people. Work is also expected to start soon here on the construction of the first 190km of a six-line metro network.

On the other side of the bay to the west of Guangzhou lies Foshan, a city of 7 million inhabitants. Foshan is already connected to Guangzhou by the Guangfo metro line, which is currently being extended at both ends, and the city also has its own metro project. Construction of Guangzhou's Line 3, which will pass through the city in a north-south direction, was due to begin last year. With a length of 74km and 35 stations, this is a massive project especially as 58km will be underground along with 30 of the stations. The line will cost Yuan 44.8bn and is expected open in 2019. Line 3 will terminate on the border with the neighbouring city of Shunde, which has its own plans to build a metro.

Foshan's 2011-2018 metro programme envisages the construction of two lines totalling 102km and costing Yuan 50bn. However, the original plans for the 70km Line 3 have been revised, which has increased the cost by Yuan 10bn to Yuan 44.4bn. This increase could mean less money is available to build Line 2 thereby delaying the project. In the long term, Foshan is planning a network of eight lines with a total length of 264km, four of which will connect the city with Guangzhou.

Trial operation began in Zhuhai in November on a 1.7km section of China's first catenary-free light rail line. The first phase of Line 1 will be 8.9km long with 14 stations and is due to open during the first half of this year. The line will eventually be extended while a second line is planned.

AnsaldoBreda has supplied the first two Sirio bi-directional five-section low-floor LRVs, with the remaining eight to be assembled by CNR. The LRVs operate using Tramwave ground power supply technology and supercapacitors developed by Ansaldo STS.

By the end of this decade it will be theoretically possible to board a metro train in Hong Kong and by changing trains from line to line travel entirely by metro through Shenzhen, Dongguan and Guangzhou to Foshan.

Inter-city links

THE Pearl River Delta is not only being connected to the rapidly-expanding national high-speed network, but it is also planned to complete a 1890km network of 23 200km/h inter-city lines by 2030 at the latest to provide fast links between the main centres within the region.

While most of the new stations are located away from the centres of the cities they serve, as it is difficult to thread the new lines through the urban areas, they are connected to the urban rail networks.

In Guangzhou, for example, the new north-south high-speed line passes to the west of the city along border with neighbouring Foshan and crosses the existing line linking the two cities. Guangzhou's new South station is located to the southwest of the city in Shibi. It has 19 tracks and 10 platforms for long-distance services plus nine tracks and six platforms for inter-city express trains. South station is currently served by metro Line 2, and from next year by Line 7. Guangzhou North station will be served by Line 9 when it opens next year.

The 145km high-speed line to Shenzhen and Hong Kong starts at Guangzhou South. The initial section from Guangzhou to Shenzhen North in the Longhua district with three intermediate stations opened in November 2011. An underground extension to Shenzhen Futian in the centre should have opened a year later, but has been delayed and is now expected to open by the end of this year. Futian will be a very spacious station with links to several metro lines.

The 30km underground high-speed connection from Shenzhen to Hong Kong will open in 2017. The new West Kowloon station with 15 tracks will be located between the existing Airport Express and West Rail stations. The station will have immigration and customs facilities for entry into China.

The initial 93km of an inter-city line on the east side of Zhujiang Bay has been operating since January 2011. It links Guangzhou South with Zhuhai North, with a 26km branch line from Xiaolan running southwest to Xinhui. A 23km extension to the centre of Zhuhai is under construction.

A new line is under construction from Shenzhen to the eastern border area of Guangzhou and Dongguan. From here another 97km new line running east to Huizhou is nearing completion, while other new routes on both shores of the Pearl River are planned.