The network includes seven major road tunnels as follows:
The Transport Agency is reviewing the management of these existing tunnels to assist in the design of future upgrades and to develop standards and guidelines to cover new tunnels. As part of the review, two projects have already been completed to provide advice on the management of air quality both in and around road tunnels, as follows:
Guidance for the management of air quality in road tunnels in New Zealand.
Stocktake of the air quality in and around existing state highway tunnels.
The Transport Agency has embarked on a programme of detailed monitoring for each of the seven tunnels, which is designed to fill in the knowledge gaps identified and develop a robust set of findings, upon which to base future tunnel management plans such as upgrades of existing tunnels and the design of new tunnels.
Tunnel monitoring campaigns are critical for ensuring that the NZ Transport Agency 'maintains and operates all air quality management/air pollution mitigation measures, such as road tunnel ventilation systems, correctly to ensure they continue to provide the designed level of mitigation' in order to meet objectives set in the State Highway Environmental Plan.
The first tunnel monitoring campaign was undertaken for the Mt Victoria and Terrace tunnels in 2008 followed by a campaign undertaken at Johnstone's Hill tunnel in 2010.