LOADING SPECTRUM EXPERIENCED BY BRIDGE STRUCTURES IN THE UNITED STATES. FINAL REPORT

More than 27,000 trucks were weighed in seven states using a Bridge Weigh-in-Motion system. The system used instrumented highway bridge girders to act as equivalent static scales to obtain truck gross and axle weights, dimensions and speed. Improvements were made in the system software and hardware such that weighing can now be performed automatically with no traffic observer necessary. The weighing operation is undetectable by truck drivers hence the results are not biased due to heavy trucks avoiding the scale. Night weighing has been performed with no danger to crew personnel or highway traffic. The accuracy of the in-motion weighing has been established by repeatability tests which show standard deviations of 1.1 kips and by comparison with static weigh stations which show standard deviations of 2.3 kips on gross weight for random traffic. Three systems have been designed, developed, tested and delivered to FHWA for operation by two crew members at the technician level with part time supervision by an engineer. Weighing rates in excess of 200 trucks per hour have been realized. The Loading Spectrum obtained for all trucks weighed at 33 sites is similar to previous studies with the exception of vehicles weighing more than 80,000 pounds for which a frequency of approximately 50 per 1000 was observed. Sixty-nine percent of all trucks weighed in this study had velocities greater than 55 mph and seven percent had velocities greater than 64 mph.