This paper presents the approach of the Retained Thickness Index (RTI) for the assessment of the residual structural integrity of asphalt pavements on the network level. Lacroix Deflectograph deflections and distress identification served as major input variables. The procedure makes use of the whole deflection basin and is not restricted to application of the maximum deflection only. The approach provides additional data on cracking origin (top-down or bottom-up) and crack propagation, and can be used in combination with the commonly used analysis methods.

The Retained Thickness Index is based on the flexural rigidity, inferred directly from the deflection bowl, and the occurrence of cracking observed in the wheelpaths. Both input parameters can be collected quite quickly.

Verification of the model was performed in 1996 on some fifty test sections of the SHRP-The Netherlands programme. This paper describes an attempt to fine tune the methodology. To this end some thirty test sections on the county network of Gelderland were made available, which is gratefully acknowledged by the authors. Analysis of Deflectograph testing, cracking surveys and asphalt coring on cracks attributed to establishing the accuracy of the predictive method.