Abstract:
For pavement design practices, several factors must be considered to ensure good performance of the pavement over the anticipated life cycle. Such factors include, but are not limited to, the type of paving materials, traffic loading characteristics, prevailing environmental conditions, and others. Traditional pavement design practices have followed the standards set by the American Society of State Highway and Transportation Officials (AASHTO) which require the use of an equivalent single axle load (ESAL - 18 kip single axle load) for design traffic input. Recently, a new mechanistic-empirical pavement design guide (MEPDG) was developed to improve pavement design practices. The guide requires the use of truck axle load spectra rather than ESAL and raises the need to improve the utilization of existing traffic data sources. The axle load spectra method is different from ESAL in that traffic loading is expressed by the number of load applications of various axle configurations (single, dual, tridem, and quad) within a given weight classification range.
Currently in Pakistan, the pavement designers convert axle weight data and combine them into an Equivalent Single Axle Load (ESAL), which cannot be used to reflect the response of the pavement material to loading. The design of pavements in the country are based on 1993 AASHTO Guide for Design of Pavement Structures, however due to development of new mechanistic-empirical pavement design methodology under National Cooperative Highway Research Program’s (NCHRP) project 1-37A, commonly referred as the 2002 Pavement Design Guide (2002 Guide), a need is felt to acquire basic design inputs. One of the key differences between the previous AASHTO design guide and the 2002 guide is the increased emphasis on the actual load per axle used for determining stresses and strains in the pavement.
To implement the new pavement design methodology in Pakistan, a detailed and comprehensive study should be carried out to address the major components of the 2002 Guide. The purpose of this study is to collect the Load Data and Vehicle Classification Count from WIM stations, which will produce traffic data for Input to the 2002 AASHTO Pavement Design Software.
