Local Road Management Manual 453 from the AASHO Road Test. The objective of the AASHO Road Test was to determine the relationship between the number of repetitions of speciifed axle loads of different magnitudes and the performance of different thicknesses of lfexible and rigid pavements built on a single subgrade. Four large loops of road approximately 3.2 km (2.0 miles) long were constructed together with two smaller loops . Each loop comprised a two-lane highway. Within each loop, test sections of a pavement with a minimum length of 30m (100 feet) were constructed. A total of 468 test sections of lfexible pavements were included together with test sections of rigid pavements. Vehicular traiffc, using specially selected and loaded vehicles with speciifc axle loads and wheel conifgurations, was allowed to move on each lane of the loops almost continuously for two years. Each lane always carried the same type of vehicle with the same axle load throughout the two-year study period but no two lanes carried vehicles of the same type and axle load. The Road Test was clearly a massive undertaking and has provided an enormous amount of data which has been analysed extensively over a 30-year period. Pavement Deterioration and Serviceability A pavement can be subjected to a number of detrimental effects including fatigue failures (cracking), which are the result of repeated stress caused by traiffc passing over the pavement. The pavement is also placed in an uncontrolled environment that produces temperature extremes and moisture variations. The combination of the environment, traiffc loads, material variations, and construction variations requires a comparatively complex set of design procedures to incorporate all of the variables. The ASSHTO pavement design procedure has been widely accepted by DPWH and around the world. It considers environment, load and materials in a methodology that is relatively easy to use. In technical terms, sealed pavement failure occurs whenever cracking, rutting or other surface distresses become visible. In contrast, the road users usually associate pavement failure with poor riding quality. Pavement engineers conducting the ASSHTO Road Test were faced with the task of combining the two failure deifnitions so that a single design procedure could be used to satisfy both observers. The Pavement Serviceability- Performance Concept was developed to address the