Limits of agreement method for comparing TSD and FWD measurements

Abstract

This article uses the limits of agreement (LOA) method to compare the falling weight deflectometer (FWD) and the traffic speed deflectometer (TSD), two pavement structural evaluation devices. The TSD measures deflection slope, whereas the FWD measures deflection. For this reason, measurements were converted to the surface curvature index (SCI) and the base damage index (BDI), which can be obtained from each device. The SCI and BDI agreement between the two devices was then evaluated. Although the relationship between the calculated SCI and BDI using both equipments is reasonably close to the line of equality, there is a significant variation and a bias in this relationship. For example, for an average SCI or BDI value of 300 μm, the bias was 30 μm (FWD values lower than TSD values), and the LOA was 380 μm.

Keywords::

• pavement deflection
• continuous measurement
• limits of agreement
• accuracy
• reproducibility

Acknowledgements

This research was performed as part of the Second Strategic Highway Research Program (SHRP 2) Project R06(F). The authors thank the UK HA for access to the HA TSD measurements and Simon Nell from the Transportation Research Laboratory (TRL) for the collection of TSD measurements. The authors acknowledge two reviewers who provided constructive comments that helped improve the article.