Evaluation of pavement service life using AASHTO 1972 and mechanistic-empirical pavement design guides

• Predicted service life (SL) using AASHTO 1972 is generally lower than M-E method. • Variation of service life is lower in M-E method than AASHTO 1972 design method. • Predicted service life using M-E method affected by location (rural vs. urban). • Predicted SL using AASHTO 1972 is affected by SN values (design and required SN). Service life is often used by state transportation agencies to evaluate alternative flexible pavement designs. The design that keeps the pavement in acceptable condition longest before it needs another maintenance treatment is the preferred design. For a given rehabilitation design, this study evaluates the pavement service life using AASHTO 1972 pavement design guide and mechanistic-empirical (M-E) pavement design guide. The service life here is referred as the duration from last completed rehabilitation to the next maintenance treatment. The goal is not to determine which method is better, but rather, it is to understand how their estimated service lives differ and what factors contribute to their differences. To perform the evaluation, rehabilitation designs developed by the SCDOT for a research project are used. These designs take into account existing pavement distresses obtained through field investigation of 28 actual rehabilitation projects on primary routes. Service life is determined using MAP-21 criteria for good and fair pavements. Analysis results indicated that (1) the predicted service life using the M-E method has lower variation than the AASHTO 1972 method and is affected by the location (rural vs. urban) of the routes, (2) the predicted service life using the AASHTO 1972 method is generally lower than that of the M-E method and is affected by the difference between the design structural number (SN) and required SN, (3) the M-E service life for good pavement is generally longer for routes that include CMRB design and the percentage of trucks lower than 10%, and (4) the AASHTO 1972 service life is higher if the existing SN is already exceeding the required SN from the previous maintenance.