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

Abstract

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.

Assessment of Continuous Pavement Deflection Measuring Technologies

“…The HA TSDThe second prototype TSD currently in operation is owned by the UK Highways Agency (HA) and operated by TRL. TRL have reported its development and performance in a recent conference papers(Ferne et al, 2009a and b). An example of typical survey results expressed over 10 m (33 ft) and 100 m (1/16 mi) lengths are provided inFigure 3-12.…”

Efficient Calibration of a Laser Dynamic Deflectometer

“…In [20], based on two years networklevel measurements, a comparison study was conducted to validate the performance of TSD. In [21]- [23], the prototype TSD was improved at the Transport Research Laboratory of UK to enable network structural surveys at 80km/h, where the geometric calibration of TSD was achieved by installing a high-specification accelerometer into the surface of a relatively strong pavement that enabled a comparative measurement of the pavement's deflection slope under TSD loading [25]. In [24], the Danish TSD was applied to measurement of the bearing capacity of 18 000 km road network in Australia, and the results showed good repeatability and no speed dependency.…”

“…However, this calibration phase was delicate and may commonly take up to a half-day to finish [18]. Improved methods were exploited in [21], [23], where accelerometers were applied to calculate the deflection under the running load of TSD. This calibration procedure involved installing accelerometers under the pavement surface, which was also complex and time consuming.…”

“…In this calibration procedure, the most important part is to calculate the angles between each of the three measuring laser Doppler sensors, i.e., L 1 , L 2 , and L 3 , and the reference laser Doppler sensor, i.e., L 4 . To gain the values of these angles, back-calculation methods were used [18], [21], [23]. The initial calibration procedure was proposed by the Greenwood company, which involved removing the five tonne lead ballast and running the TSD over a stiff concrete pavement.…”

Enhanced Sensing and Data Processing System for Continuous Profiling of Pavement Deflection

“…In order to continuously measure pavement deflections at higher speeds, extensive efforts have been carried out over the past decades. The continuous deflection measurement technologies currently in use are the Traffic Speed Deflectograph (TSD) [1,2,3,4,5], Rolling Wheel Deflectometer (RWD) [6,7,8,9,10], Quest Integrated/Dynatest Consulting Rolling Weight Deflectometer [11,12], Road Deflection Tester (RDT) [13,14], and the Rolling Dynamic Deflectometer (RDD) [15]. In January 2018, Dynatest Raptor (Rapid Pavement Tester) was introduced to the Transportation Research Board (TRB).…”