Study of multiple presence probabilities for trucks using recent weigh-in-motion data

An important parameter that controls the maximum load imposed on the structure is related to the number of simultaneous vehicles on the bridge, which is determined through data on truck headways under operating conditions. Accurate headway information should be collected through WIM systems. Simultaneous data on headways and weights is necessary to determine possible correlations between truck positions or the lanes they occupy and their weights or other characteristics such as truck type, size and numbers of axles. Fortunately, the data needed for multiple presence estimates is presently available and already contained in the raw data files captured by many WIM data loggers. Under NCHRP Project 12-76, five WIM sites in New York State were studied in order to determine the maximum multiple presence probabilities for various truck traffic volumes. Maximum multiple presence probabilities were obtained for each headway separation interval and compared with past assumptions. These statistics can be used to simulate multiple-presence events for sites where accurate time stamps are not available. The paper will describe the findings of this study.