Lyttelton Tunnel will be down to one lane overnight on Thursday so contractors can clean it.
The cleaning operation will be carried out betweem 8pm Thursday and 6am Friday.
“This is part of standard maintenance for the tunnel, reducing it to one lane around the maintenance crew,” said Transport Agency Journey Manager Lee Wright. “There will be slight delays for road users due to the single lane operation.”
Fuel tankers and other carriers of dangerous goods are not allowed access during the time the tunnel is being cleaned.
Dangerous goods transport which requires tunnel closures will be allowed to pass through the tunnel in the hour immediately before and after the maintenance period.