Edge details for use with porous asphalt were promulgated in HA 79/97 in Volume 4 of the Design Manual for Roads and Bridges before their effectiveness was completely proven because of the need to give designers the best available advice. Further work has now been undertaken and the results from both a series of in-situ measurements of relative hydraulic conductivity on existing edge details for sections of road with porous asphalt and a programme of laboratory tests on each of the edge details is reported. The in-situ measurements were of the relative hydraulic conductivity across the pavement near different edge details after different times in service. These measurements showed significant reductions with time, particularly during the first year, and slight differences of behaviour close to the edge. There are indications that drainage edge details with free edges may clog more slowly than those details with enclosed systems, but more data are needed to validate this observation. The laboratory trials allowed more detailed and controlled measurements to be made to gain a better understanding of the behaviour. These trials have shown that, at rainfalls above 11mm/h on 14m carriageways, the water flows over, as well as through, the porous asphalt. Nevertheless, the various drainage systems investigated all performed successfully with porous asphalt surfacings. (A)

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