Mechanistic-empirical equivalent single axle loads for urban pavements

The deregulation of the trucking industry in the mid-1980’s resulted in the growth of commercial vehicles not only in number, but also in weight, size and dimension. As a result, road agencies are finding their road networks being subjected to commercial vehicle load spectra greater than those initially projected. The augmented load spectra, combined with the aged state of many in-service roads, are resulting in the accelerated deterioration of our roadway infrastructure. Although much empirical evidence exists regarding the performance of rural pavements subjected to various types of loading, there is a lack of knowledge regarding the operation of commercial vehicles within the urban environment and their ensuing effects on urban roads. Urban municipalities are therefore beginning to realize the importance of identifying and quantifying the effects of commercial vehicle operations (CVO) on urban road assets, traffic congestion and motorist safety. Due to the limitations of conventional Equivalent Single Axle Loads (ESALs) when applied to urban pavements, this research aimed to investigate commercial vehicle load equivalencies for various classes of urban roadway in the City of Saskatoon. Urban load equivalencies were created by combining a traffic load spectra from a typical freeway in the City of Saskatoon with structural deformation and damage responses measured across several urban roadways. This established a framework for calculating the responses incurred from commercial vehicle loading across different types of urban roads. Based on the results of the mechanistic-empirical urban load equivalency analysis performed in this research, urban ESAL factors (ESALFs) for local-industrial roadways were found to range from 50 percent less than to 250 percent greater than conventional load equivalencies. Urban arterial ESALFs ranged from 20 percent to 260 percent greater than conventional load equivalencies. The primary response-based ESALFs for urban local and collector roadways ranged from 150 to 700 percent greater than conventional load equivalencies. The large range in mechanistic-empirical ESALFs across urban road classes indicated that typical urban roadways are much more sensitive to heavy vehicle loads than their rural highway counterparts. In a test urban traffic application, it was calculated that a typical low floor transit vehicle was capable of producing loads ranging from a minimum of nine ESALs on urban local-industrial roadways to a maximum of 140 ESALs on urban local and collector roadways