ON-SITE CALIBRATION OF WEIGH-IN-MOTION SYSTEMS

The importance of on-site calibration for weigh-in-motion systems has been illustrated by comparing weigh-in-motion weight estimates, made after calibrating the system by three different calibration-loading patterns, against corresponding wheel weights measured on a special static reference scale. Various truck types selected from the traffic on I-10 near Seguin, Texas, were included in the analysis and high, intermediate, and low speeds of in-motion weighing were considered. A pronounced improvement in the accuracy with which weights were estimated by the high and intermediate systems was achieved when six loaded five-axle tractor-trailer trucks, chosen randomly from the traffic stream, were used as the basis for calibration compared with multiple runs of the same loaded two-axle, single-unit test truck. The variability in weigh-in-motion weight estimates was not affected appreciably by the type of moving vehicle loading that was used as the basis for calibration. Static-weight loading is recommended for low speeds of weigh-in-motion calibration, and moving-vehicle loading is recommended for practicable on-site calibration of higher-speed weigh-in-motion systems. Suggestions are offered on the types of trucks and the minimum number of wheel loads that should be used as the basis for on-site calibration.