The damaged Auckland Harbour Bridge was due to reopen around 9am, after being closed for repairs overnight.
The Transport Agency Waka Kotahi says a new permanent strut to replace the one that was buckled by an overturned truck two weeks ago, has been successfully installed.
The steel strut - nearly 23-metres long - was delivered in two pieces.
A like-for-like replacement made in Whangārei, it's painted to match the rest of the bridge.
Engineers will now carry out tension work, to return the bridge's weight distribution to its usual balance. That work will take several days.
Three lanes are being opened in each direction, however, the two centre lanes will remain closed.
The Transport Agency says it's a significant step towards getting the bridge fully repaired and operational again.
It says the damage caused when a truck was blown over in 120km/h winds on 18 September was unprecedented in the bridge's 61-year history.