The Laboratory has since carried out an extensive program of testing on construction sites. Early results from this program are presented which indicate that pavement stiffness is important but which also confirms that other non-structural factors increase the risk of failure. Cores taken from the surfacings established that slippage is strongly associated with a lack of shear near the interface between the basecourse and the wearing courase. This lack of strength is produced during construction. The report describes a full-scale experiment designed to identify any interaction between pavement stiffness and effects related to surfacing temperatures during laying and early service life. From laboratory tests an assessment of the role of the binder has also been made.