Permeable public roads: Reducing runoff and stormwater issues

In 2014, VCS Denmark opened Denmark’s first 100 % permeable public road, Agerlandsvej in Odense.

Paved with porous asphalt, the road captures surface runoff (and stormwater in more extreme cases) and lets the water seep to a stone aggregate reservoir underneath. The reservoir temporarily stores the water before infiltrating it into the subsoil.

Permeable pavement is a unique and effective way to address local surface runoff issues and support sustainable growth. Permeable roads provide a brand new approach to planning infrastructure in urban areas – an innovative alternative to the more conventional expansion of sewers.

Odense has a large percentage of combined sewers, which makes any solution that removes or delays surface runoff to the sewers attractive. Permeable paving is just such a solution.

Construction and maintenance

The stone aggregate beneath the asphalt is specially developed with materials from local Danish gravel pits. It has the same carrying capacity as traditional base course but with 30% voids between the materials, which can be used as a reservoir.

The permeable pavement requires frequent maintenance with a sweeping and vacuuming truck to prevent grit, gravel and other material from clogging the open pores of the asphalt. This also means that sand can not be used as winter road maintenance as is often the case in Denmark.

The local residents are informed about the importance of maintaining the road and are urged to keep it free from debris and waste from their gardens and homes.

Groundwater protection

Groundwater pollution is a major concern in Denmark, where water supply is mainly groundwater based. Infiltration water from permeable construction is considered just as polluted as roadwater runoff.

The permeable road is located in a groundwater protection zone, where infiltration of untreated roadwater runoff is normally not allowed. In this case, however, an exception is made because the road is a cul-de-sac with a very low traffic load.

For the sake of groundwater protection, salt is not allowed for winter road maintenance of the permeable road.

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