The two main types of road surface in New Zealand are chipseal and asphaltic concrete. The latter is generally confined to high volume urban roads. For high volume, high speed roads, open-graded porous asphalt, known as friction course, is preferred.
This project, carried out between 1995 and 1997, compares the performance of two sizes (14 mm and 20 mm) of open-graded asphalt laid on a road section when first laid and after periods of wear. The performance, in terms of noise reduction, skid resistance and permeability, was monitored at construction and after 6, 12, 17 and 24 months. An adjacent site of 14 mm friction course, which had been in place for about eight years, was also monitored. Recommendations for improvements to future studies are made.