Mass Rapid Transit System in Delhi
At the time of independence, the population of Delhi was a mere 0.6 million. Starting from this humble figure, the population of the metropolis grew to 5.7 million in 1981, 12 million in 1998, and 13.78 million in 2001. In the absence of an efficient mass transport system, the number of motor vehicles in Delhi has increased from 3 million in 1998 to about 5 million in 2006. The large number of vehicles lead to congestion on roads, which leads to a slowing down of vehicular speeds, thereby resulting in fuel wastage, increased air pollution, and an increase in road accidents.
It is a well-known fact that out of all the cities in the country, the process of urbanization has been the fastest in Delhi. The city witnesses about 11.7 million transit trips per day, of which no less than 62% are by public transport. Among the various public transport options available, 99% are road based and only 1% are rail based, despite the fact that Delhi has 144 route kilometres of rail tracks converging into the city from five different directions.
In 1989 a study for an MRTS network for Delhi was undertaken at the instance of the Delhi Government. The report brought out the urgent need for a rail-based transit system comprising a network of 181 route km that consisted of 29.5 km of underground alignments, 40.5 km of elevated route, and 111 km of surface/elevated route length. Nearly 99 km of the route length was analogous with the existing rail network and was proposed as a surface (or at-grade) corridor. This scheme, which was the basis of the Delhi Master Plan 2001, however, remained unimplemented.
Corridors for MRTS
There are two distinct types of corridors planned for the MRTS in Delhi.
Rail corridor The system is basically located on the surface (at-grade) or on elevated ground and works on 25-kV ac traction and consists of a rolling stock with sealed doors and windows that remain closed while in motion.
Metro corridor The system is underground except for depot connections and lines, which may be partly at-grade.
1 Phase I of Delhi Metro System
Once the Government decided to take up the Delhi metro project, the Delhi metro rail corporation (DMRC) was set up in 1995 for the implementation and subsequent operation of the Delhi MRTS. The DMRC, however, became effectively functional in 1998, after the appointment of general consultants and a team to execute the project.
Before starting with the implementation of the project, the corridors included in phase I were reviewed and it was finally decided to include three corridors covering a route length of 62.1 km, which included 12.1 km of underground, 38.2 km of elevated, and 11.8 km of at-grade alignment (Fig. 29.4). The first phase of the Delhi metro system consists of three lines, as presented in Table 29.1.
The Government decided to take up the first phase of the metro system in August 1996. The project was started in right earnest in 1998 and was completed in December 2005.
2 Technical Details of Delhi Metro
The Delhi metro is planned on the lines of a world class metro and is equipped with modern communication and train control systems. In the Delhi metro system, trains are available at a three-minute frequency during peak periods. The entrances and exits of metro stations are monitored by flap doors operated by smart cards. For the convenience of commuters, an adequate number of escalators are installed at the metro stations. A special feature of the Delhi metro will be its integration ultimately with other modes of public transport, enabling the commuters to interchange between one mode and another. The technical details and design parameters of the Delhi Metro system are briefly described below.
The rolling stock is the mainstay of a metro rail system. Metro coaches are lightweight, air-conditioned coaches with stainless steel bodies that are equipped with features such as three-phase ac motors. All systems in the coach are monitored by a microprocessor-based train integrated management system (TIMS). All coaches are of the same type and each coach is able to accommodate nearly 380 passengers. The coaches have a width of 3.2 m and an overall length of 22 m (including sitting and standing passengers).
Some of the important features of the metro rolling stock are listed below.
(a) Automatic electric door closing mechanism.
(b) All doors fully open within 2.5 sec and fully close within 2.5 to 3.5 sec.
(c) The train cannot move unless all the doors are properly closed and automatically locked.
(d) The train can be halted with the application of the emergency brake, should a door open during running.
(e) Emergency evacuation facility in the form of emergency front door.
(f) Emergency illumination and ventilation in the case of a power failure.
The initial plan involves running four-coach trains, each consisting of two motor
coaches that are out fitted with propulsion equipment and two driving trailer coaches, with a total carrying capacity of 1500 passengers. Subsequently, six-coach and eight-coach trains are likely to run to meet increasing traffic demands. These trains are planned to run at an average speed of 32 to 35 km/hr over an average interstation distance of 1.1 to 1.3 km.
Signalling and train control
Delhi metro trains are provided with the latest signalling technology and control system as described in the subsequent paragraphs.
Signalling It has been decided that the trains plying underground and in surface corridors will run at a 3-minute interval in peak hours. The signalling system is designed for an ultimate headway of two minutes, with a continuous automatic signalling system comprising of the following special features.
Automatic train protection Automatic train protection will consist of cab signalling, whereby the drivers will get information as regards the condition of the line beforehand and so that they can control the speed of the trains in advance as per the track status or obstruction. Normally the driver will apply the brakes in the case of any perceived obstruction on the track. In case a driver fails to do so, the emergency brakes are applied automatically and all these events are recorded in the appropriate system device for the purpose of establishing accountability.
Automatic train supervision Automatic train supervision (ATS) is a sophisticated computer-based supervisory system, which will take over the critical functions of the controller in the control room and will drastically reduce the workload of the station master. The assistance of ATS is necessary in cases where trains run at a close headway of 2 minutes. The train describer system of ATS displays the positions of the trains while they are in motion in visual form in the control room as well as provide precise information with regard to passengers.
Automatic train operation This feature is required to be provided for underground corridors only. It enables the train to be driven without any human intervention, thereby providing a high level of operational efficiency.
Interlocking of yards An advanced interlocking system with high-speed (50 km/ hr) turnouts has been recommended for the yards. The entire section is to be circuited with audio frequency track circuits, which should eliminate any failures on account of the insulated joints giving way, thus requiring replacement.
Telecommunication The telecommunication network between various stations and services is like a backbone of optic fibre, which will have an enormous capacity for channelling data and voice communication. It will carry all train control information through telemetry links, which will bear the details regarding the running of the train and also the data collected by the passenger information system.
Passengers information system In the system that has been proposed, the central train describer will provide precise information to the passengers at every platform on a real time basis by furnishing online information through the central computer. All the stations will be provided with centrally synchronized clocks on the various platforms to maintain time standards. The public address system will enable centralized as well as local announcements on all stations platforms.
CCTV system Closed circuit TVs are provided at all the critical locations in the station premises to monitor every safety aspect.
To ensure the continuous availability of quality power for the running of metro trains, the utmost efforts have been made to plan and design a power supply system with the degree of reliability found in other world class metros. The Delhi metro system derives its operating power in the form of 25-kV ac traction.
The design standards for the track of the metro system are briefly described in the following paragraphs.
Spacing of tracks The metro routes consist of two broad gauge tracks spaced 4.10 m apart, which is less than the 4.725 m standard spacing on Indian Railways. The reduced spacing has been feasible due to the fact that the doors of the coaches are closed and none of the doors open outward as is the case with the goods wagons of Indian Railways. The points and crossings are 1 in 12 and 1 in 8.5, as in the case of Indian Railways.
Gradients The steepest gradient permissible is 3.0%. Gradients steeper than 2.5% are adopted only in exceptional cases.
Curves Curves of radius less than 450 m are adopted sparingly on running lines. No curve on a running line may have a radius less than 300 m.
Tracks on stations On stations, tracks are not to be laid on gradient steeper than 0.1% (1 in 1000) and they should also not be laid on curves with radius less than 1000 m. Vertical curves normally have a radius of 2500 m at points where there is a change in the gradient. In the case of transition curves, the rules followed are the same as those on Indian Railways. The other features of the metro track are as follows.
(a) The metro track consists of 60-kg UIC rails on level tracks, which rest on concrete sleepers and are fixed using elastic fastenings (Pandrol clip mark 11). The sleeper density is 1660 sleepers per km.
(b) The ballast cushion is prepared using hard stone ballast and measures 300 mm in thickness.
(c) 60-kg head hardened rails have been used to enhance the service life of the rails, particularly on sharp curves and steep gradients.
(d) To minimize the need for track maintenance and reduce the dimensions of structures that are consequential to the quality of the run, a 'ballastless track' is being laid on elevated sections, viaducts, and tunnels. These stretches are provided with 60-kg rails that are fixed with the help of Vossloh fastenings.
(e) To improve the standard of maintenance and ensure a comfortable ride, rails are mostly welded as long welded rails and efforts have been made to ascertain that the entire track is almost 'joint-less'. For this purpose, even the turnouts have been integrated into the long welded rails. Specially designed turnouts are used with thick web switches and CMS crossings by means of welded leg extensions.
There are about 53 metro stations, including 12 underground stations on phase 1 of the Delhi metro. Metro stations are normally two-line stations with side or island platforms. The platforms are 185 m long, so as to accommodate eight-coach trains. The platform surface lies 1.08 m above the rail level, so that the floor of the coaches is almost level with the platform. The width of the platform is normally 6 m in the case of side platforms and 10 m in the case of island platforms.
Tracks at stations with side platforms are placed 4.1 m apart, while these with island platforms, are placed around 13.3 m apart. Stations located in well-populated areas are normally spaced 1 km apart. The interstation distance can, however, vary marginally to suit site conditions.
Stations situated on an elevated corridor along the central verge of the road can be provided with tracks at a height of about 12 m above the road level. Most of the underground metro stations are generally two-level stations between 270 m to 300 m in length. A typical station is 20 m wide and 15 m deep. The first level boasts of various passenger facilities together with ventilation and electronics and communication equipment rooms and the lower level comprises the platform with electric equipment rooms at each end of the box. Island platforms are provided with stations that are adjacent to board tunnel sections while side platforms are provided with cut and cover tunnels. All stations have been designed with the option to accommodate platform screen doors.
3 Civil Works
Some of the new technologies and innovations in construction techniques that are being deployed for the Delhi MRTS are briefly mentioned here.
Construction of bridges
Several innovative construction techniques were used in the construction of the bridges. For example, a new Yamuna bridge (12 spans of 46.2 m each) was constructed using modern techniques during the construction of the Delhi Metro. The substructure of this bridge consists of capsule-shaped piers that rest on well (caisson) foundations of 10 m diameter with a steining thickness of 1.0 m, which have been sunk up to a depth of about 39 m. The 'jack-down' method, supplemented with air/water jetting, has been used for sinking the wells. This method involved pushing the well assembly down into the ground by applying pressure to counter the resistance arising due to skin friction around the periphery of the wells and below the cutting edge. Soil dredging has been carried out inside the well simultaneously. The new techniques resulted in the faster sinking of the wells. Also, the wells have been sunk plumb into the water with the help of minimum tilts or shifts.
The superstructure of the bridge comprises of a single box girder of a constant depth of 3.5 m that has been launched using an incremental launching technique. This technique involved casting the girder on the bridge approach behind the abutment in segments of length 23.1 m, which is half the length of one span. Each segment has been cast behind the previous unit. After a sufficient concrete strength was attained, the new unit was post-tensioned to the previous one. The assembly of units was pushed forward to permit the casting of the succeeding segment. This technique resulted in a single continuous girder of a length of 554 m with no joints.
The innovative features of the Yamuna bridge are summarized below.
(a) Second incrementally launched bridge in India, the first being the Panvel Nadi bridges of the Konkan Railway.
(b) First box girder in India carrying dual unballasted tracks.
(c) An innovative technique for sinking the wells; the jack-down method has been adopted for sinking 15 wells. Ground anchors have been installed near the well staining, which have been used for taking the reaction of the specially designed hydraulic jacks at the top.
The elevated viaduct simply comprises of supported spans with lengths varying from 21.1 m to 29.1 m. It has been constructed by the precast segmental technique with epoxy bonded joints and traditional internal pre-stressing. The span lengths have been determined mainly on the basis of the site constraints at the ground level for the location of the foundations and piers. All precasting has been done at a centralized casting yard.
An aesthetic form of the substructure has been evolved so as to harmonize with the flow of the forces. In this structure the pier gradually tapers outward at the top to support the bearings under the box webs. All the piers have been cast in place using rigid steel which was poured in a single attempt in order to avoid any construction joints. The use of bolts in the concrete has not been permitted. Bored piles of a diameter of 1.2 m that have been cast in situ have been included by employing modern hydraulic rigs. To ensure a standard span, groups of nine piles with a length of 23 m to 28 m have been stacked in the soil. In rocky terrains, piles have been stacked in the rock in groups of six up to a depth equal to 1.5 to 3.0 times the diameter of the pile, depending on the type of rock encountered. A temporary casing has been employed for the stabilization of the bore holes.
Cut and cover tunnels
It is possible to construct tunnels by excavating the ground surface, hence the cut and cover method has been employed for tunnel construction in these stretches. Cut and cover tunnels are generally designed as a single structural unit with a dividing wall, and walkways for each track giving an average box width of 10 m. The over-run tunnels are used as sidings and contain three tracks while at the depot spur the tunnels contain four tracks. The construction methodology for cut and cover tunnels is similar to that of cut and cover stations.
Cut and cover construction, though economical, results in a lot of public inconvenience if planned improperly. As such, it requires exhaustive planning with regard to utilities, traffic management, and environmental concerns such as cutting of trees and air and noise pollution.
Bored tunnel construction
The bored tunnel construction technique has been used at many places in the metro corridor tunnels. The internal diameter of such tunnels is about 5.6 m and they are generally lined with precast reinforced concrete segments. Tunnel boring machines (TBMs) have been used in place of conventional tunnelling methods that employing various hand mining techniques, since conventional tunnelling methods suffer from major handicaps with regard to slower progress and risks to existing structures in the vicinity of tunnel excavation.
Since the bored tunnel construction for the Delhi metro involved tunnelling through both quartzite and soft ground, two types of TBMs have been used, namely, rock TBM for rocky ground and earth pressure balance machine (EPBM) for soft ground. In the case of an EPBM, the excavated face is supported by pressurizing the soil that has been dug up, together with additives if necessary, to give it a plastic texture. A screw auger is used to remove the excavated material. The earth pressure within the cutter head is maintained by balancing the rate at which it advances with the rate at which the spoil material is removed and adjusting the parameters as required. The gap between the excavation surface and the precast concrete lining is filled by means of an automatic injection from the tail of the machine, which minimizes ground settlement. Watertightness at the tail is ensured by injecting grease into the three rows of brush seals.
4 Underground Versus Elevated Alignment
Underground construction is a much costlier option than elevated alignment. The current average cost per route kilometre for construction on an elevated alignment, including stations, rolling stock, signalling, and electrical equipment as well as land and incidental works, is Rs 1000 million as compared to Rs 3000 million for underground construction. On account of the vast cost difference, the choice of underground construction is restricted to areas where elevated alignment is not suitable. In the case of Delhi metro, underground construction is restricted to the core area of Delhi on the North-South and East-West corridors, which intersect in the Connaught Place area. Most of the route length outside the core area is likely to be constructed as an elevated route.
In the case of elevated segments of the MRTS, the alignment on city roads usually follows the central verge of the road. Piers of about 2 m diameter are spaced 20-30 m apart along the central verge. The arrangement of girders above the pier cap is shown in the general arrangement given in Fig. 29.5. Tracks are generally laid 8.5-9.5 m above the road level on elevated routes outside the station. The desirable minimum width of the roads for locating an elevated MRTS on the same is 30 m, although a road width of 40-45 m is preferable. The geometry of the road should be favourable for the adoption of curves adhering to the minimum MRTS standards. In the case of underground construction on stretches outside the station, the rail level lies at a minimum depth of 9 m below the road surface. This is done with the object of 2-3 m of space below the road for electrical cables, telephone cables, and drains.
A corridor need not be wholly underground or elevated. An underground corridor in the core city area could get converted into an elevated corridor in the outer parts, where the conditions are favourable for such constructions. It is crucial that an extra stretch of aligned road surface be available between the point where the underground section ends and the elevated section starts. The alignment in this stretch should rise from about 9 m below the ground to 9 m above the road level. In order to ensure that the length of the at-grade stretch is not unduly long, the tracks are provided with a steep gradient for negotiating this difference in the level. This stretch can measure 400-500 m in length depending on the site characteristics.
In the at-grade stretch, the MRTS tracks are walled on both sides, their outer faces being nearly 10 m apart. This implies that the road width is effectively reduced by about 11 m on this stretch. This factor is of great importance in choosing the location for an at-grade ramp.
Schedule of dimensions
The Delhi Metro Rail Corporation has drawn up a schedule of the dimensions for its system. These dimensions should normally be adhered to when undertaking new works and finding alternatives to existing works on BG lines (1676 mm), except in exceptional cases where the sanction of the commissioner of railway safety has to be specifically obtained.
5 Delhi Metro Phase II
The Delhi Metro Rail Corporation has already made plans for phase II of Delhi metro (Fig. 29.5). The total route length is about 54 km as per the details given in Table 29.2.
Table 29.2 Details of phase II of Delhi metro
The preparation of detailed project reports for the corridors of phase II of the Delhi metro is complete and the Government of Delhi has already made budgetary provisions for the same. Work on phase II is scheduled to be completed before 2010.
With the success of the Delhi metro, several state governments have approached the DMRC for preparing detailed project reports for metros for their cities. Such reports have already been prepared for Bangalore and Hyderabad and submitted to the Karnataka and Andhra Pradesh state governments, respectively. Investigations/ studies are presently underway for the preparation of detailed project reports for constructing metro rail systems in Mumbai, Ahmedabad, Kolkata, and Kochi.