MECHANISTIC-BASED ESALS FOR URBAN PAVEMENTS

Equivalent Single Axle Loads (ESALs) have been the standard traffic loading measure used in highway engineering and pavement management practices for decades. However, there are several significant limitations to the application of conventional ESALs for engineering and managing urban pavements systems under modern field state conditions. The objective of this research was to investigate the use of a typical urban load spectra analysis with weigh-inmotion, as well as falling weight deflection pavement structural response assessment methods, for developing mechanistic-based structural impact load equivalencies that specifically address traffic loading urban field state conditions. This research employed a four-lane weigh-in-motion system installed on Circle Drive within the City of Saskatoon, Saskatchewan, to measure commercial truck load spectra operating across a primary arterial within the City. This research also employed dynamic falling weight deflection measurements taken across standard roadway classes within Saskatoon’s road network within the typical range of commercial vehicle load spectra experienced in Saskatoon. The deflection data was integrated with the results of mechanistic frequency sweep characterization of conventional City of Saskatoon road materials in order to differentiate the effect of traffic speed. The commercial load spectra data, primary falling weight deflection measurements and frequency sweep characterization of Saskatoon hot mix asphaltic concrete (HMAC) were integrated to develop mechanistic primary response-based commercial vehicle load equivalency ESAL factors for different classes of roadways and commercial vehicles within the City of Saskatoon. This research found that the historic method of estimating pavement design life ESAL’s may be highly inaccurate for urban field state conditions. This research found that conventional load equivalencies may be up to 700% low when compared to actual pavement primary responses under modern day urban field state conditions. Given the increasing truck traffic as observed in urban centres across Canada, it is recommended that urban road managers adopt mechanistic-based ESALs to more accurately assess the actual field state loading impacts that may be occurring in the field.