![]() Results confirmed that the conventional AASHTO 93 method predicts faster deterioration of pavement conditions over time, while the results of AASHTO 93 Plus method better aligned with the field data. The total number of 3,726 IRI data records of these 518 pavements were converted to PSI and then compared to those obtained from the traditional AASHTO 93 and AASHTO 93 Plus methods for validation. The results showed that the new material-specific layer coefficients were well above the typical value of 0.44. to a depth of at least 5 feet below proposed subgrade elevation (10 feet below. Five-hundred-eighteen (518) flexible pavements from USA and Canada roads and 1599 HMAs from the Long-Term Pavement Performance (LTPP) database were analyzed. Standards and the AASHTO Guide for Design of Pavement Structures (1993). ![]() Part I includes background material to assist the user in the proper interpretation of the design procedures and to provide an understanding of the. Material on overlay design methodology and rehabilitation, including seven overlay procedures and associated options is included. The reliability level is not included directly in the AASHTO design equations. The AASHTO 93 Plus method considers viscoelasticity and temperature-dependency of asphalt mixtures to estimate the layer coefficient. This book provides approaches to pavement design including design and management principals, procedures for new construction or reconstruction, and procedures for rehabilitation of existing pavements. AASHTO design method accounts for these uncertainties by incorporating a reliability level R to provide a factor of safety into the pavement design and thereby increase the probability that the pavement will perform as intended over its design life. This paper presents a four-step procedure (called AASHTO 93 Plus method) to determine structural layer coefficients of asphalt mixtures. However, many agencies use a single layer coefficient for asphalt mixtures and pavements are currently designed with inaccurate values, as proved by many. Since the release of the AASHTO 1993 design guide, many aspects of pavement design have changed, including asphalt material properties, traffic, environmental factors, etc. Many road agencies worldwide still use the empirical AASHTO 1993 pavement design method.
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