Tunnelling work for a 6-kilometre missing link of the Mumbai-Pune Expressway began on Monday after a symbolic inauguration by Maharashtra PWD minister Eknath Shinde on Sunday.
The plan envisages building twin tunnels to reduce the 19-kilometre distance of the expressway between Khopoli Exit to Sinhgad Institute by 6 kilometres, said officials.
Tenders for the tunnelling work were given to two private firms in August last year, they added.
Shinde said the tunnel, with a width of 24 metres, is among the widest in the world, and said commuting between two of Maharashtra's biggest cities would ease out considerably once the link is ready in three years time.
The project is estimated to cost Rs 6,695 crore and will also have a 900-metre bridge and a cable-stayed structure of 650 metres, officials added.
The Mumbai Pune Expressway is presently a 6-lane cement concrete road with a length of 94 kms. It meets National Highway 4 at Khalapur Toll Plaza, and separates near Khandala exit.
The stretch on which the expressway and highway meet is a bottle-neck as vehicles from two major roads converge on a narrow connector, prompting authorities to think of the missing link.