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 Initial & terminal serviceability indices must be established to compute the change in serviceability ( DPSI) in the design equation. Pavement ability to serve traffic at some instances during its life. PSI is a surrogate measure for PSR (present serviceability rating) PSR is based on panel of engineers rating (subjective) PSI is based on physical measurement of pavement roughness using special equipments (objective) Procedure was developed to determine the present serviceability index (PSI) of the pavement based on its roughness and distress which were measured in terms of extent of cracking, patching, and rut depth for flexible pavements. To quantify pavement performance, a concept known as the serviceability performance was developed. The main factor considered under functional performance is riding quality. These factors include: cracking, faulting, raveling, and so forth.įunctional performance: is an indication of how effectively the pavement serves the user. Structural performance: related to the physical condition of the pavement with respect to the factors that have negative impact on the capability of the pavement to carry the traffic load. Traffic Subgrade soil properties Materials of construction Environmental effects Drainage Reliability Pavement Performance (Loss of serviceability). This method Incorporates various design inputs including :    Data were thoroughly analyzed and the results formed the basis for the AASHTO method  ِِInterim guide was published in 1961, revised in 1972, further edition 1986, then 1993ĪASHTO Design Method/ Design Considerations   Longitudinal and transverse profiles were obtained to determine extent of rutting, surface deflection caused by loaded vehicles moving at very low speeds,  Pavement curvature at different speeds, stress imposed on the subgrade and temperature distribution in the pavement layers.

Vehicles were driven for thousand repetitions (single axle ( 2, 000 – 30, 000 lb) and tandem (24, 000 – 48,000 lb).ĭata were collected from pavement with respect to extent of cracking and amount of patching required to maintain the section in service. Flexible: HMA surface (1-6 “), well-graded crushed limestone base (0-9”), and uniformly graded sand-gravel subbase (0-6”). Tangents sections with different lengths (> 100 ft). Rigid & flexible A-6 subgrade Four lane divided highway loops. Many types of test section were prepared and tested. It is an effort that was carried out with the cooperation of all states and several industry groups. Chapter 16: Highway Engineering, by Paul Wright & Karen Dixon, 7th Edition, Wiley & sons Instructor:ĪASHTO Method/ Introduction         īased on the results of AASHTO road test conducted on Ottawa, Illinois. Flexible Pavement Thickness Design / AASHTO Method Source: Chapter 20: Traffic & Highway Engineering by Nicholas Garber and Lester Hoel, Third Edition, Brooks/Cole.