<![CDATA[Reliable road-roughness monitoring typically requires dedicated profilers, whose cost and operational complexity can limit repeated surveys. This study characterized the sensing chain of a vehicle-mounted Ultrasonic Surface Roughness Meter (USR) developed as a lower-cost alternative for International Roughness Index (IRI) data acquisition. The component evaluation included 15 ultrasonic distance tests under stationary and horizontal-motion conditions, 15 accelerometer tests referenced to 9.806 m/s², and GPS distance checks against roadway kilometer references and vehicle speedometer measurements. To strengthen the evaluation, the component results were re-expressed using error-based metrology metrics rather than relying solely on internal consistency statistics. The ultrasonic subsystem achieved a mean absolute error of 0.174 cm, an RMSE of 0.187 cm, and a mean absolute percentage error of 1.07% relative to ruler measurements; all reported relative errors were below 2%. The accelerometer subsystem achieved a mean absolute error of 0.0252 m/s², an RMSE of 0.0327 m/s², and a mean absolute percentage error of 0.257% relative to the 9.806 m/s² reference value, with the largest observed relative error of 0.75%. GPS distance evaluation showed confidence levels above 96%, with correlations of 99.84% against kilometer-point distance and 99.80% against speedometer-derived distance. These results indicate that the sensing chain provides a sufficiently stable measurement foundation for subsequent IRI computation and field validation while demonstrating that component-level accuracy should be assessed separately from end-to-end road-profile agreement.]]>
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