DECEMBER 24 marked the 10th anniversary of a truly groundbreaking urban transport system. Described as the largest infrastructure project in the history of the Indian state, Delhi Metro drew heavily on the experience of other operators from around the world, notably MTR Corporation in Hong Kong, hired consultants from abroad, and adopted international construction methods and proven technologies to build a safe, efficient, high-capacity transit system as quickly as possible.

The speed of development is a crucial factor in the success of the system. Delhi is one of the fastest-growing cities in the world - the population increased by 21% between 2001 and 2011 to 16.75 million, and is forecast to reach 24.32 million by 2021.

There are also other important demographic shifts that support large-scale metro development. Land use is changing dramatically, with the commercialisation of previously residential areas, and increasing suburbanisation as the promise of higher living standards lures families away from the central districts, fuelling the emergence of commuter culture.

At present only around 20% of people in Delhi own a car, but with an average of 1335 new cars registered in the city every day in 2011, the road network is under increasing strain. The problems don't stop when you reach your destination - in central Delhi around 11% of the land area is required for parking, which is already an acute and largely unregulated issue.

To prevent the city being completely overwhelmed by road traffic, a coordinated programme of mass transit investment was clearly required which would provide an affordable and convenient alternative to the car. Delhi built 65km of metro in the first phase, which was completed two years and nine months ahead of schedule in 2005 at a total cost of $US 2.3bn. By 2010 the completion of Phase 2 had expanded the network to 187km.

The metro now carries more than 2 million passengers a day and Delhi Metro Rail Corporation (DMRC) says demand is increasing constantly. A record 2.289 million passengers were carried on February 11, when the metro surpassed a record set only three months previously. Trains are being lengthened from six to eight cars to ease pressure on the busiest sections of the network. A total of 68 eight-car trains are being introduced on lines 2 and 3, the first of which entered service on Line 2 in December, increasing capacity by up to 600 compared with the equivalent six-car set.

delhimetroHowever, keeping up with population growth demands much more than longer trains, and after a decade-and-a-half of relentless construction, Delhi has embarked on an ambitious third phase, which will add a further 137km to the network by 2016. DMRC regards this as one of the most crucial stages of development, improving connectivity to large parts of the city not currently served by the metro while relieving the four principal interchanges on the existing network and providing desperately-needed additional capacity in the core.

Two completely new lines will follow the city's main arterial roads and DMRC says these will be the first in Delhi to employ unattended train operation (UTO), with platform screen doors at stations.

Line 7 follows the route of the inner ring road from Mukundpur to Shiv Vihar, tracing an almost complete circle around the western, southern and eastern edges of the city on a mostly elevated alignment. The 58.3km line will link all of the existing lines with no less than 10 interchanges, easing the pressure on the handful of existing hubs such as Central Secretariat and Rajiv Chowk by offering alternative routes across the city which avoid the most congested stations.

DMRC and its contractors have encountered a number of constructional challenges on this project, not least ensuring traffic on the ring road continues to flow as smoothly as possible. These include raising high-voltage power lines over the elevated alignment at Punjabi Bagh, and the construction of Dhaula Kuan station, which crosses the Airport Express Link at a height of 23m above street level.

The 36.4km Line 8 will follow the outer ring road south of the city from Janakpuri West on Line 3, skirting the northern perimeter of Indira Gandhi International Airport before heading east to Hauz Khas and Kalindj Kunj, where a new depot will be constructed. The line will then bridge the Yamuna River to terminate at an interchange with Line 3 at Botanical Garden in Noida. Line 8 will have 26 stations, 12 of them underground, and 19km of the route will be elevated or at grade with the remaining 17.3km in tunnels.

DMRC has opted for six-car trains on both of these lines, but with peak headways of 2min 15s and a commercial speed of around 35km/h, hourly capacity will be higher than on existing lines.

The 9.4km seven-station extension of Line 6 from Central Secretariat to Kashmere Gate will run entirely underground and will interchange with Line 3 at Mandi House and Line 1 at Kashmere Gate. The opening of line will relieve Rajiv Chowk station, which is the busiest on the network handling more than 500,000 passengers per day. The initial 3km section as far as Mandi House is due to open next year, although DMRC indicated recently that services could begin running before the end of 2013.

The 4.5km northern extension of Line 2 from Jahangirpuri to Badli is also due to be completed next year, while construction is underway on a 14km elevated extension beyond Badarpur which will serve Faridabad, a satellite city in the neighbouring state of Haryana.

Three other extensions were also approved last year for inclusion in Phase 3, including Line 1 from Rithala to Bawana (12km); Line 5 from Mundka to Bahadurgarh (11km); and a branch off Line 3 from Dwarka to Najafgarh (5.5km).

A foundation stone was laid on February 9 to mark the start of construction on the Mundka - Bahadurgarh section, which will follow Highway 10 on an elevated alignment with seven stations. Civil works will commence in July and commercial services are due to start in March 2016. The line is expected to carry 143,000 passengers per day in 2016, rising to 197,000 in 2021.


A key feature of Phase 3 is the extent of tunnelling required. Phase 1 involved the construction of 13km of tunnels and 13 underground stations, while 34.9km of tunnels and 18 underground stations were constructed in Phase 2. Phase 3 alone requires the construction of 41km of tunnels and 28 underground stations, meaning almost 40% of the network will be underground by 2016. The longest underground section being constructed in Phase 3 is a 17.3km tunnel between IG Domestic Airport and Kalkaji on Line 8.

This means around 25 TBMs are being used, compared with 14 in Phase 2, and a centralised control centre has been established to monitor tunnelling activity across the city, tracking the progress of each TBM by GPS. DMRC is also trying to move away from cut-and-cover construction, which has been hugely disruptive to traffic in the crowded streets, and is experimenting with different techniques for underground stations. Where street closures are unavoidable, DMRC has modelled traffic flow to establish the best diversionary routes.

Another challenge facing engineers is the need to bore new tunnels above or below operational metro tunnels, the first time this has been done in Delhi.

Despite some delays in planning approvals and land acquisition, DMRC said in January it remains confident all Phase 3 projects will be completed by March 2016. The opening of these lines is expected to push daily ridership beyond the 4 million mark, and a total of 486 new metro cars are being procured to provide the necessary capacity in the train fleet.

India's urban development minister Mr Kamal Nath indicated in December that construction could begin on the fourth phase of the metro before the completion of Phase 3, reflecting the need to keep pace with the growth of the city. Phase 4 will involve the construction of 120km of new lines, expanding the network to 440km by 2021 and bringing every home in the city will within 500m of a station.