Comparative measurements of ground penetrating radars used for road and bridge diagnostics in the Czech Republic and France

•In-situ comparative measurements of GPR systems.•Accuracy of measurements: pavement layer thickness and reinforcement position.•Recommendations for performance of GPR comparative measurements. The paper describes the current situation regarding the comparative measurement and accuracy of ground penetrating radars (GPR). GPR measurements are used for non-destructive diagnostic of roads and bridges, specifically for measuring pavement layer thickness and determining the location and position of reinforcement in concrete. The information used in the paper is based on the performed in-situ measurements. The conclusion includes recommendations of how to perform and evaluate the in-situ GPR comparative measurements.