The Lyttelton tunnel is being shut a dozen times a day so dangerous goods that should be sent via a coastal road can go through it.
The February 2011 earthquake made parts of Evans Pass Road along the coast between Sumner and Lyttelton impassable.
The tunnel is being used as an alternative but has to be shut to other traffic when goods such as fuels and explosive materials are transferred.
The New Zealand Transport Agency has confirmed the tunnel is being shut 12 times a day, on average.
The Christchurch City Council, Port Lyttelton and the Transport Authority are working on options to repair Evans Pass Road - but it is not yet certain who will meet the bill of up to $120 million.
