Metro rail has transformed travel in Delhi, Mumbai, Bengaluru and many other Indian cities, and urban rail moves millions of people a day in London, New York and Tokyo. Behind the smooth ride lies a carefully engineered system of power, braking and signalling.
Where the power comes from
Metro trains are electric. Depending on the city and line, they draw power in one of two main ways:
- Overhead wire at high voltage alternating current, collected by a pantograph on the roof. Many Indian metro lines use 25 kV AC overhead lines.
- Third rail beside the track carrying direct current, commonly around 750 V, collected by a shoe on the bogie. This avoids overhead wires in tunnels.
Onboard electronics convert this power to drive efficient AC traction motors on several axles, spreading the pulling force along the train.
Braking that makes electricity
When a metro train slows down, its motors work in reverse as generators. This regenerative braking turns the train's motion back into electricity, which is fed to other trains accelerating nearby or back into the supply. Because metros stop every couple of kilometres, this recovers a significant amount of energy over a day.
Signalling: keeping trains apart
Older railways divide track into fixed blocks, allowing only one train per block. Many modern metros use communication-based train control, or CBTC. Trains constantly report their exact position by radio, and the system calculates a safe braking distance in real time. Trains can then run much closer together, which allows trains every couple of minutes at peak hours.
Driverless trains
With CBTC and automatic train operation, some metro lines run without drivers. A control centre supervises every train. Platform screen doors line up with train doors, preventing people from falling onto the track and making automatic operation safer.
The civil engineering
- Elevated viaducts built from precast segments assembled by launching girders, minimising road closures.
- Tunnels bored by tunnel boring machines that dig and install concrete lining rings as they move.
- Stations designed for crowd flow, ventilation and fire safety, often the most complex part of the project.
Frequently asked questions
Why do metro trains have so many motors?
Spreading motors across several cars gives better grip, faster acceleration and redundancy if one motor fails.
Is the third rail dangerous?
Yes, it is live. That is why tracks are fenced, stations have screen doors in many cities and the public must never enter the track area.