The changes in the rheological properties of petroleum bitumens after the addition of ethylene-vinyl acetate co-polymer (EVA) are described and the consequent effect on their use in rolled asphalt wearing course mixtures is reported. In particular, the changes in the Marshall stability and deformation resistance using four asphalt sands of different stability are quantified. The relationship between these properties and the effect of the EVA component is discussed in detail, and equations are derived relating the Marshall stability of a conventional rolled asphalt wearing course to the Marshall stability of a rolled asphalt containing bitumen modified with 5 per cent EVA for the same resistance to permanent deformation.