The structural strengthening brought about by laying pervious macadam surfacings on existing roads has been assessed by using linear elastic theory to compute the stresses and strains induced in the pavements by vehicle loading before and afetr surfacing with the pervious macadam. These computations predicted a significant reduction in the magnitude of stresses and strains after surfacing, a result which was confirmed in practice by direct measurement on a full-scale road pavement. Stress and strain computations were then used to determine the structural contribution of 40 mm of pervious macadam surfacing in terms of equivalent thicknesses of rolled asphalt surfacing and rolled asphalt and dense bitumen macadam roadbases for the present recommended designs of road pavements