The NZ Transport Agency is strengthening Penrose bridge on the Southern Motorway against vehicle strikes.
The bridge has been hit 41 times since 2008, with 32 smashes on the southbound side.
Collision protection beams are being installed to protect the State Highway 1 structure from further damage.
“The four-span bridge is made of reinforced concrete, but vehicle strikes damage the concrete beams and risk undermining the structural capacity of the outer beams. Repairs are costly and disruptive to motorway users,” the NZTA says.
The bridge at its lowest point over the southbound lanes has 4.52m clearance. NZ Transport Agency rules stipulate that the maximum height for a load is 4.25m.
In May 2016, a 15 tonne digger on the back of a truck set off the detection system before it hit the bridge.
The crash blocked two lanes for about three and a half hours, causing significant disruption to Auckland traffic.
The Transport Agency has an over-height detection system on the motorway, but the driver of a detected vehicle still has to pull over and stop.
The collision protection beams are a last resort measure to protect the bridge.
Installation of the protection beam on the northbound lane was completed this week The beam on the southbound side will be installed in April.
