a range of wearing-course materials suitable for the maintenance of bituminous roads is being compared in a full-scale experiment laid on trunk road a1 at buckden in cambridgeshire during 1975 and 1976. they include open-textured macadam, pervious macadam, dense bitumen macadam, delugrip materials, rolled asphalt and a surface dressing. their performance is being assessed from measurements of deformation, deflection, riding quality, texture depth, sideway-force coefficient, braking-force coefficient, permeability, void content, noise and spray and this report gives interim results obtained during the first two years of trafficking. all the wearing-course materials gave good resistance to deformation, good riding quality and, because aggregates of high polished-stone value were used, good resistance to skidding at low speed (50 km/h). the surface dressing, pervious macadam and well-chipped rolled asphalt provided adequate texture depth and showed little reduction in braking-force coefficient for an increase in speed from 50 to 130 km/h whereas the delugrip materials, dense bitumen macadam and open-textured macadam, unable to maintain a substantial texture depth, showed a 20-40 per cent reduction. some of these low-textured materials proved to be permeable to water. it was also found that they contributed less to the recorded traffic noise and, except for the open-textured macadam, generated more spray than those with deeper texture.(a)

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