Site-specific truck loads on bridges and roads

Condition assessment of bridge structures, prediction of remaining life and evaluation of pavement performance and behaviour require knowledge of load and resistance statistical parameters. The present study addresses the need for the determination of live load on bridges and roads, and in particular the site-specific variation of the live load statistics. Truck loads were measured under normal traffic conditions at selected bridges located on interstate highways, state highways, US highways and surface streets using a bridge weigh-in-motion (WIM) system. Truck data is also available from highway weigh station logs and citation files. Stationary weigh station data is biased and may not accurately reflect the distribution of truck axle weights, axle spacing, and gross vehicle weight. Citation data is helpful in understanding the nature and extent of overloaded trucks; however, it will not be representative of the normal traffic distribution. WIM measurements of trucks can be taken discretely during normal traffic conditions, resulting in unbiased data for a statistically accurate sample of truck traffic travelling a particular highway. Results of the present study show that truck loads are strongly site specific. In addition, there is a negative correlation between law enforcement effort and the occurrence of overloaded trucks. Overloaded trucks are observed on roads not controlled by truck weigh stations. A comparison of the weigh station data, truck citation data and WIM measurements obtained in this study confirms this observation.