Statistical Evaluation of Truck Overloads

This paper examines statistics of truck overloads on highways. An overload is defined as a load that exceeds the legal truckload limit. The overload statistics depend on truck types; each is specified by the number of axles. The truckload spectra examined in this paper reveal that overloads generally appear with a distinctly different pattern than that in lower load levels. This is especially true among trucks with five or more axles. To derive a theoretical probability distribution model to represent different patterns in a load spectrum, mixed distribution models are introduced in this paper. A mixed distribution is made of two different functions, each representing one of the different patterns appearing in the load spectrum. These functions are linearly combined and adjusted to represent the overloads and all other loads statistics properly. Using the statistics of overloads, along with a damage estimation model, one can determine to what extent overloads are responsible for damage done to bridges and highways. The probability of occurrence of specific truck weights exceeding the legal load limit can be used to estimate the frequency of occurrence of heavier loads in transportation facilities and thus determine the damage potentials of overloads. This information can be used along with routine engineering analyses that many pertinent state agencies conduct when issuing truck‐overload permits.