Development of a Calibration Procedure for the U.K. Highways Agency Traffic-Speed Deflectometer

One of the headline objectives of the U.K. Highways Agency (HA) is to reduce congestion and improve road safety while undertaking necessary highway maintenance. To this end, HA has invested significant resources in developing an appropriate technology to collect road condition and structural data at traffic speeds. This is reflected in the recent procurement for HA of a prototype traffic-speed deflectometer (TSD). The machine, originally developed by Greenwood Engineering A/S of Denmark, exploits the Doppler effect by using lasers to measure pavement deflection velocities under the loaded wheel of a truck. As part of a research program at the U.K. Transport Research Laboratory, the TSD is being developed to undertake structural surveys at traffic speeds. This paper describes the operation of the TSD and continues with a discussion of one of the most challenging aspects of the research program: the development of a calibration procedure. The proposed procedure compares the response of a particular section of road to the TSD, as recorded by an accelerometer embedded in the road pavement, with that recorded by the Doppler lasers on the TSD.