c. 2024 pitt & sherry


A non-invasive way to assess road pavement strength.

Measuring pavement deflection under the application of a known axle load whilst travelling at approximately 3-4 kilometres per hour along a traffic lane – pitt&sherry’s deflectograph truck measures the pavement deflection in both the inner and outer wheel paths of the traffic lane providing valuable information regarding the pavement strength. This information combined with traffic volume and composition information can then be used to estimate the residual life of a pavement, target subsurface investigations or optimise pavement rehabilitation treatments. We are one of the very few organisations in Australia to own and operate this effective tool used to assess pavement strength, inform the management of road pavement assessments and to facilitate optimisation of pavement rehabilitation design treatments.

What is a deflectograph?

A deflectograph is a powerful tool that provides an efficient, automated, non-destructive method for evaluating the structural condition of a pavement. Mounted on a sled under the chassis of a host truck, the deflectograph’s two beams measure the deflection in each wheel path as the test wheel approaches. The deflectograph records deflection from the centre of the test load in a series of tests at longitudinal spacings at a constant speed.

How does it operate?

Depending on the type of surface being tested, a deflectograph travels at a testing speed of 3–4 kilometres per hour. The travel speeds are controlled to maximise the quality of the test data, with up to 16 lane-kilometres of testing able to be undertaken in a normal working day (depending on traffic conditions and the number of set-ups). Testing can be undertaken during the day or at night on sealed roads at any time of their design life. Traffic management measures are assessed on a site-specific basis.

What can it do?

By capturing a continuous ‘look below the surface’ along a road or on a road network, a deflectograph survey enables us to predict future condition of the pavement and estimate its residual life. It also provides critical information that can be used in the selection of rehabilitation treatments.


It is common for decisions regarding the allocation of road maintenance funding to be based on information collected only on the road surface. This often leads to inappropriate and costly rehabilitation treatments being selected—either at the time of application or later, after their premature failure. This often means that maintenance funds are not used to maximum benefit on the road network. A deflectograph provides considerably more data than other pavement deflection measuring techniques for a given length of road, enabling more accurate estimates of residual life and informed decisions regarding pavement rehabilitation treatments. On sections of a road network where strengthening is required the deflection information can be used to design the thickness of overlay necessary to extend the life of the road, improving performance. Alternatively, on sections of the network where deflections are low, resealing can be undertaken to address skid resistance and other surface issues with confidence. The benefit of a deflectograph survey can be realised in a single project, or within a year-long road maintenance program. The deflectograph can undertake surveys from a few lane-kilometres to thousands of kilometres, with typical commissions ranging from 6 to 20 kilometres.

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