The NZ Transport Agency says the toll road will remain open in both directions at all times but one of the two tunnels will be closed during the maintenance period and all traffic will be diverted into the alternative tunnel.
Speeds through the tunnel will be reduced to 30kph and motorists should take extra care both approaching and inside the tunnels, which they will be sharing with oncoming traffic.
The closures have been timed to coincide with the lightest traffic volumes to minimise the disruption to drivers.
The closures are necessary to ensure the tunnels are kept in a safe and high standard for all road users.
The work will also involve tests for the state-of-the-art safety equipment installed within the tunnels, including the fire, ventilation and public address systems.
- Northern Gateway Toll Road (State Highway 1) at Johnstone Hill Tunnels closed 0600 Monday 22 February until 0400 Friday 26 February
- Northbound traffic will be diverted into the Southbound tunnel early on Monday morning, and Southbound traffic will then be diverted into the Northbound tunnel early on Wednesday morning.