A time-lapse video has shown the scale of work involved in building Auckland's Waterview tunnel connection.
NZ Transport Agency's highway manager Brett Gliddon said the $1.4 billion project was running on schedule and should open some time in early 2017.
The 2.4-kilometre tunnel is the largest road project ever undertaken in New Zealand.
Footage from the video shows the removal of spoil from the tunnel, before it is taken to Wiri in south Auckland where is it used to fill in a disused quarry.
It also shows construction of the interchange to connect the Southwestern (SH20) and Northwestern (SH16) motorways.
The tunnel-boring machine "Alice" has travelled more than 1500 metres at a depth of 30m as of July 14.
A two-week stoppage in mid-May forced "Alice" to undergo maintenance but the timeline of the tunnels was still on track, Gliddon said.
Construction of the tunnels is due to be completed in late 2015.
After that it will be fitted out with mechanical and electrical systems before being available for motorists to use.
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