The NZ Transport Agency (NZTA) is strengthening Penrose bridge on the Southern Motorway against vehicle strikes.
The bridge has been hit 41 times since 2008 so NZTA is installing collision protection beams to protect the bridge 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 bridge outer beams. Repairs are costly and disruptive to motorway users.
The bridge over the southbound lanes has 4.52m clearance at its lowest point. NZTA rules stipulate that the maximum height for a load is 4.25m.
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.
In May 2016, a 15 tonne digger on the back of a truck set off the detection system before it hit the Penrose bridge. The crash blocked two lanes for about three and a half hours, causing significant disruption to Auckland traffic.
Installation of the protection beam on the northbound lane was completed last night (26 February 2017). The beam on the southbound side will be installed in April.