Vertical Pavement Strain as Means of Weighing Vehicles

The concept of estimating vehicle loads by weigh‐in‐motion systems that monitor deflections in strain‐gaged bridges and culverts is well established. In this project, the possibility of estimating loads by monitoring subgrade deflections in flexible pavements was investigated. A line of vertical strain transducers was installed at a depth of 500 mm in a dense sand subgrade across one wheel path of the outside lane of a busy highway (this research was conducted in Australia, where the outside lane is on the left). The installation was calibrated with a truck of known weight, enabling the weights of other vehicles to be calculated and compared with weights determined by other means. Four test runs were conducted at six month intervals. Repeatability, sources of error, and accuracy of weight prediction are discussed. Successful results were obtained with the system, but further work would be required before it could be used as an operational system.