Abstract Manager

The Pavement Mechanistic-Empirical Design (PMED) software integrated mechanistic responses of pavement structures due to applied repeated loads and the resulting accumulated damage with empirically observed distresses to predict pavement performance. Understanding the sensitivity and trends of PMED software predictions due to key design variables is essential for informed decision-making in pavement design and management. As one of the multi-year software evaluation design trials by the Transportation Association of Canada (TAC) ME Pavement Design Subcommittee, the objective of this study was investigating the effects of traffic loads in terms of annual average daily truck traffic (AADTT) and asphalt concrete (AC) layer thickness on PMED software predicted distresses in new flexible pavements.

Design trials and analysis were completed in 2025 for four traffic load levels (2-way AADTT of 1250, 2500, 5000 and 7500) and four AC layer thicknesses (150mm, 180mm, 210mm and 240mm) to quantify and assess their influence on key pavement performance indicators, including total rutting, AC layer rutting, thermal cracking (TC), bottom-up fatigue cracking (BUFC), top-down fatigue cracking (TDFC), and international roughness index (IRI). All design simulations were conducted using data from 11 Canadian weather stations to capture regional climatic variability. All other inputs including granular base and subbase properties and thicknesses, subgrade properties and design reliability remained fixed in all trials.

Preliminary analyses indicate that total rutting and AC layer rutting are highly sensitive to variation of AADTT and they decrease with increased AC thickness, with more pronounced impacts in colder climatic regions than the warmer climates. Higher AC layer rutting was observed in some relatively colder climates (NB, QC and AB) as compared to warmer climatic areas, which is unexpected. Thermal cracking performance improved with increased AC thickness, while the influence of AADTT on thermal cracking was minimal, which is as expected. In general, both BUFC and TDFC were strongly influenced by the variation of traffic loads, with incremental improvements associated with thicker AC layers. However, in some regions, increased AC layer thickness (e.g., from 170mm to 200mm) resulted in increased BUFC, which is unexpected. The predicted IRI is primarily governed by the variation of predicted other distresses in pavements.

The objective of this paper is to present the details of the study, results, analysis and findings. These will provide valuable insights into the sensitivity and trends of PMED software predictions and support ongoing efforts to enhance performance prediction, design reliability and calibration considerations within Canadian context.