A second road tunnel between Christchurch and Lyttelton will be needed in about 20 years because of growth in freight transport, the port boss says.

Lyttelton Port Company chief executive Peter Davie said an engineer's "guesstimate" put the cost of a second tunnel at about $500 million, and funding it would probably fall to road control authorities.

"I always say with long term infrastructure you have got to plan for it early. So you have got to say, 'if we have got this volume of cargo in 20 years' time, how are we going to handle it'?"

Davie said the logical thing would be for one tunnel to serve port traffic, possibly bypassing Norwich Quay in Lyttelton and connecting directly to the port.


New Zealand Transport Agency southern region director Jim Harland said the tunnel could accommodate further growth in traffic volumes before a solution would be needed.

Increasing use of rail to the port would also help.

"The second tunnel has been discussed as part of the Greater Christchurch Freight Management Study, and was suggested as a long-term option, subject to a comprehensive business case analysis at the appropriate time," Harland said.

NZTA is expected to install a deluge system in the tunnel by the end of next year, involving sprinklers that could be activated in response to a vehicle fire.

The tunnel will be down to one lane tonight from 9pm, to 2am on Friday, while maintenance is carried out. Dangerous goods carriers will not be able to go through the tunnel, but other drivers will be escorted.