Trains are the main form of travel for most people in Mumbai - one of the most congested cities in the world.
Trains carry millions of people a day to and from the suburbs
Every day about six million people travel on the city's Suburban Railway system. Renowned for being uncomfortable, it is nevertheless described as the city's lifeline.
The Mumbai line has the highest passenger density of any urban railway system in the world - travellers are literally squeezed in like sardines, making it hard to breathe, especially when it is hot.
But it is still quicker - and in most cases cheaper - than travelling by road, where it can sometimes take all day to get from one side of the city to the other.
In a city short of travel choices, travelling by train is the best way to commute and it is not uncommon to see the wealthiest businessman travelling alongside the poorest street trader.
Mumbai's rail system is estimated to carry more than half of the total daily passenger capacity of Indian Railways - which is itself hailed as the busiest such network in the world.
The lines are among the most crowded in the world
Both the Mumbai Suburban Railway and the Indian Railways network originate from the first railways built by the British in India from the mid-19th Century onwards, making it one of the oldest railway networks in the world.
Experts say that the line is now being stretched to the limit.
The morning rush hour starts from 0400, as people try harder and harder to beat the crowds in their travels from the suburbs into the city.
The evening rush hour does not finish on most days until about 2030.
By 0800, commuters jostle and elbow their way into trains. Managing to barge one's way into a carriage is judged as an achievement of sorts.
On the positive side, Mumbai trains are usually on time, carriages are reserved for women and fares are not regarded as excessive.