The Traffic Speed Deflectometer (TSD), is an innovative Rolling Wheel Deflectometer measuring pavement response to applied load. The unique TSD technology is developed by Greenwood Engineering and has initiated a shift of paradigm in pavement engineering worldwide.
The Greenwood TSD provides continuous bearing capacity results at project and network level while following the flow of traffic. This makes the Greenwood TSD highly cost-effective.
The TSD provides repeatable, detailed and accurate data, from which bearing capacity indices can be derived and pavement fatigue / residual life can be estimated. This information is essential to decide how and exactly from where to where to repair.
International studies show major savings and more cost-effective road maintenance when plans are based on structural data and focus is kept on repairing the underlying reasons of the road problems, instead of only dealing with the symptoms on the surface.
The TSD quickly identifies the weakest road section, which allows for correct timing in preventive maintenance.
As the TSD is measuring while following normal traffic speed, it is possible to measure hundreds of kilometers per workday. And because the TSD is operated by only two persons – a driver and an operator – it has no need for assisting personnel closing road lanes or setting up road markings up etc.
This makes the TSD very effective and more economic per measured kilometer compared to traditional point-measuring equipment.
The Traffic Speed Deflectometer measures the velocity of deflection rather than displacement. To measure the pavement-motion, the TSD uses the principle from the Doppler effect where the movement of a signal-source is creating a change in the wavelength created by the source.
In the TSD, the Doppler lasers are sending out a well described signal, which when reflected from the moving pavement has changed wavelength depending on the pavement velocity.
In this way, road surface texture and roughness, have no influence on the accuracy of bearing capacity measurements with the TSD.
For new TSDs, ten or more Doppler lasers are installed to measure the pavement-motion in front of and behind the load wheel to picture the full deflection bowl.
The TSD provides the full picture of the deflection bowl with well-known values like Surface Curvature Index 300 (SCI 300), maximum deflection (d0) and more. This can be achieved when Doppler lasers are installed both in front of and behind the load wheel and in the longitudinal centerline between the twin tyres of the trailer.