The truck with superpowers

The TSD, Traffic Speed Deflectometer, truck in operation.

High-tech truck measures highway surfaces to detect problems before they become more expensive to fix.

It looks like a regular semi-trailer truck, but its insides packed with lasers and computers making it one of the most precious loads on our roads, valued at about $3.7 million.

About the only outward clues for motorists to the long white beast's road-surveying superpowers are two video cameras on its rear, and warnings of invisible radiation from downward-pointing 3D lasers.

The cameras and lasers, designed to detect surface cracking, are among four sets of diagnostic weapons the Australian-based truck is lending the Transport Agency in a "stitch in time saves nine" hunt for weaknesses in the country's state highways.

Instead of having to dig up entire stretches of road after pot-holes break out, early detection of damage caused by water seepage and compounded by heavy loads should mean only having to reseal their surfaces.

"Once you've got a pot-hole, effectively you've got to rip up the road and start again," says Garry Warren, general manager of Australia's research-based ARRB Group, which is running the first round of a five-year contract with the Transport Agency to put our state highways - and a handful of local roads - under the rack.

"You can't maintain what you can't measure and now we can measure the amount of damage that's being done," Mr Warren said.

Five more lasers about halfway under the 15-metre truck are measuring roughness, texture and rutting in up to 12,000km of road lanes which the vehicle is covering through much of New Zealand.

But the kicker for engineers is an array of seven Doppler lasers measuring deflections or movement in the road surface, and the rate at which it recovers from being run over by a 10-tonne ballast-enhanced load on the truck's rear axle.

That has required special permits to exceed the maximum legal load of 8.2 tonnes and, although the truck generally powers along at up 80km/h, it has to ease up when it is approaching bridges.

Its main lasers use the "Doppler effect" in which red light is emitted at a certain frequency and then returns at a different frequency, similar to how sirens on fire engines, ambulances or police cars vary in pitch between their approach to and departure from a listening point.

The first, located 3.5m in front of the axle, is a "reference" laser to measure the road before it comes under pressure, and the others are at varying distances within 900mm of the wheels to gauge its resilience as the load rumbles over it.

"It's almost the holy grail for pavement engineers - it's the most sophisticated piece of equipment that's ever run on our roads," says Mr Warren.

Although Danish company Greenwood Engineering has also developed seven other "traffic speed deflectometer" vehicles with Doppler lasers, his is the only one in the world to which so much extra diagnostic fire-power has been added.

The Transport Agency's share of its services follows first-year runs under contracts with roading authorities in Queensland and New South Wales, where it has clocked about 35,000km.

Mr Warren said the previous method of measuring sub-surface weakness was to drop loads from a stationary position.

"But you can't do that for an entire network because it's very slow, and it's dangerous - you have to stop the [survey] vehicle, drop the weight, then do it again in another 50m."

Although it is too early to forecast savings in New Zealand's annual $1 billion road maintenance budget, Transport Agency highways and network operations group manager Tommy Parker expects the truck's information harvest to help his staff prioritise funding decisions based on need, to ensure the safety of road users.