The speed limit around Auckland's Waterview Tunnel will be increasing to 100km/h from next Monday.

The NZ Transport Agency has announced it will be increasing the variable speed limits on sections of State Highways 16 and 20 around the tunnel to allow maximum speeds of 100km/h in certain driving conditions.

Variable speed limits mean that the maximum legal speed limit can change between 30km/h and 100km/h and can be adjusted for the road and driving conditions.

NZTA acting system design manager Kevin Reid said speed limits are likely to be reduced during peak periods when there are typically high traffic volumes and in the event of incidents, crashes, maintenance work or extreme weather conditions.

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The first phase will happen on SH16 between St Lukes and Rosebank and on SH20 between Maioro St and Dominion Rd.

The second phase, on SH16 between St Lukes and closer to the central motorway junction, will follow at a later point once further work on signage and system requirements has been finalised.

"The Transport Agency takes adjusting speed limits very seriously and we have appreciated people's patience while the necessary investigations, consultation and legal processes were completed," Reid said.

Speed limits in the Waterview Tunnel and its approaches will not change, remaining at 80km/h maximum to manage the higher risks associated with an enclosed tunnel environment.