KEY POINTS:
Workmen last night began demolishing the old Onewa Rd onramp bridge after it was damaged by a truck carrying a digger.
The incident yesterday morning caused a giant snarl-up on the Northern Motorway and closed the southbound lanes.
It left chunks of concrete and reinforcing rods on the roadway.
The gridlock was so severe police advised drivers to turn their engines off and read in their cars.
The southbound lanes finally reopened about 2.30pm, but closed again at 8pm so the bridge could be demolished overnight. It had been due to be pulled down in two months and was not in use at the time of the crash.
New Zealand Transport Agency acting regional manager Tommy Parker said there was no danger of the bridge collapsing.
Motorist Andrew Redwood was among the thousands caught up in the chaos. "The digger went all the way through. There's steel and concrete all over the place."
Recommendations to southbound motorists to use the Upper Harbour Expressway and the Northwestern Motorway brought little relief.
One motorist reported taking 40 minutes to get from Albany to the Greenhithe bridge and a further hour to reach the city.
The Transport Agency gave permission for a southbound bus lane from Esmonde Rd to past Onewa Rd to be opened up for ordinary vehicles at 11am.
Diversions will be in place while the overbridge demolition is in progress. It is hoped to have it completed by midday today.
Accidents in other parts of the region added to yesterday's traffic woes.
A three-car crash near Warkworth just before 10.30am left one person with serious injuries and several others with cuts and bruises.
