Thane-Borivali second tunnel work begins amid 15-minute travel promise

Workers are building a very long underground road tunnel in Mumbai, India.

Two giant digging machines called tunnel boring machines are being used.

The first machine, named Nayak, started working about two months ago.

The second machine, named Arjuna, has just started digging its own tunnel.

Now both machines can dig at the same time, which speeds things up.

The tunnels will be about 10.25 kilometres long and will go deep beneath a big park called Sanjay Gandhi National Park.

Right now, driving between Thane and Borivali takes about an hour or even an hour and a half.

When the tunnels are finished, the same trip should take only around 15 minutes.

Less time stuck in traffic also means less fuel used and less smoke in the air.

The people in charge say this will be India's longest and deepest city tunnel.