An improved warning system has been installed on Auckland's Southern Motorway to reduce the number of high vehicles crashing into Penrose Bridge.

The NZ Transport Agency has just finished installing and testing six new generation electronic signs to warn drivers who risk of hitting one of the region's lowest highway overbridges at Ellerslie-Penrose.

"Bridge strikes cause delays that can affect many road users, creating disruption and financial losses to drivers and businesses, which is why we're consistently developing ways we can reduce the chances of these incidents happening," says Brett Gliddon the Transport Agency's Auckland Highway Manager.

Lowest bridge on the network

At 4.57m the Penrose Bridge is one of the lowest bridges on the Auckland motorway network. Without a specific permit the maximum height for vehicles on the motorway is 4.25 metres – this means that anything that hits the Penrose Bridge is illegally overheight.

Penrose Bridge has been struck four times so far this year, with thirteen strikes in total across the Auckland motorway network.

Sensor system

The warning system is triggered by sensors at either side of the motorway that scan and check the height of passing vehicles. If a vehicle is overheight warning messages are displayed on the new signs and the event is logged for further investigation.

"The new system gives drivers travelling either north or south two warnings, and an opportunity to leave the motorway system and avoid the bridge. Those that don't exit will then be given a third and final warning to pull over or stop prior to the bridge itself."

"The final sign will instruct all traffic to stop. It is a very clear warning that evasive action is needed, it will be very difficult to miss or ignore."

Warnings hard to miss

The new signs are larger and more visible than the original signs and display coloured messages which research shows are highly effective at attracting attention.