A flexible pavement evaluation and overlay design procedure has been developed by the Transport and Road Research Laboratory (TRRL) . The majority of the information used to derive the relationships contained in this procedure was collected on medium and heavily trafficked roads. Very little performance data existed prior to the start of this project for lightly trafficked roads, with the result that the relationships in the above procedure had to be extrapolated at the lower traffic levels. This investigation has resulted in the setting up of a large data base containing pavement condition, construction and strength information. A new methodology has been developed for investigating the performance of flexible pavements based upon data gathered over a limited time scale. This methodology has been used to relate deflection to pavement condition and the subsequent relationships used to validate those published by TRRL. The work has added confidence to the use of the evaluation and overlay design procedure for roads that have carried low volumes of traffic. An investigation has also been undertaken into the use of deflected shape measurements, made with a Deflectograph, to characterise pavement construction. Theoretical studies have been made using a finite element approach, together with practical studies based upon deflected shape measurements recorded on a number of lightly trafficked roads. Resulting from these investigations, a method has been developed for estimating the thickness of bituminous material in a flexible pavement from measurements of deflected shape recorded with a Deflectograph. Such an estimation procedure would in the long term remove a major obstacle to on-board real-time processing of deflection measurements recorded with a Deflectograph. In the short term it would help eliminate a great deal of uncertainty that exists at present concerning the pavement construction between locations where cores have been removed.

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