Highway pavement with high functioning Experience shows that porous asphalt is generally very resistant to rutting deformation. The main difficulty is clogging with detritus, which reduces the spray-suppression. However, even when it is heavily clogged, considerable spray- and noise-suppression remains (Daines, 1992; Nicholls, 1997). The main difficulty is clogging with detritus, which reduces the spray-suppression The rate of clogging is very variable : a major factor affecting the rate of clogging is the amount of detritus prevalent, which is very variable-10§® and 14§® varieties of porous asphalt in northern France and Holland have not become heavily clogged, which has been ascribed to the pumping action of heavy vechicles in wet weather Some successful de-clogging of porous asphalt using a "Hydrovac" machine has been carried out in Austria The durability of porous Asphalt has been found to be considerably better than was expected Long-term experience in the United Kingdom is very limited, but based on trials carried out in 1984, it was concluded (Daines, 1992) that ; Based on experience to date, 20 §® porous Asphalt using 100 open unmodified bitumen with 2% of hydrated lime as filler and a binder content of 3.7% will last in excess of 7 year under 4000 cvd with effective spray reduction Porous Asphalts with higher binder contents (which can be achieved with certain modifiers) will probably last significantly longer, but they will have reduced hydraulic conductivities In some continental countries, considerable amount of porous asphalt have already been in service for more than ten years under unlimited heavy traffic Thus, it is clear that the durability of porous asphalt is at least good enough to make it a viable surfacing material, with a service life comparable with that of dense asphalts