More frequent cloudbursts and resulting cascades of concentrated rainwater require still bigger and more expensive sewers in Denmark in the future - we often hear that. But is this really true?
No, it is not! – in September 2015, the Municipality of Aalborg could reopen a road in the district of Nørresundby as a so-called climate road, and this solves the problems with a quite cheap solution.
The designation ‘Climate road’ used for the 1.7 km road is the expression for a new type of construction technology and choice of materials, developed by NCC Roads, road division of the construction company NCC, to counter the cloudburst problem.
14,000 square meters of climate road
Earlier, smaller test sections with this type of road construction have been performed on closed residential roads in the Danish cities Odense, Billund and Farsø, but the 14,000 square meters of road in Aalborg is by far the largest and most busy road to be established as a climate road in Denmark. The climate road serves Nørresundby's industrial area Troldholm and Stenholm, and - at least for city busses - also the expanding Aalborg Airport.
Climate changes have become part of the reality in the municipality of Aalborg. As a consequence, the Municipality has prepared a responsible climate policy, and with the establishment of the new climate road, the Municipality has acted on this policy.
The water runs through asphalt
In the daily life, road users do not notice any difference except that they will not run into any sewage covers, because unlike in traditional roads, there are no sewer lines under the perma road. This is because the asphalt used is a special "perforated" type, a so-called perma-asphalt.
The rainwater can penetrate this asphalt regardless the amount of water in that the construction under the asphalt, including 40 cm DrænStabil (drain stable), a special mixing of crushed stones, is built up of an unusual type of base layers. This provides a road base leaving much more space for water collection than usual – in fact up to 30 percent or 300 liters per cubic meter of gravel allowing the water to flow through. Even a cloudburst of 120 mm rain over a short period of time will not leave as much as a puddle on the road. For the new road Lufthavnsvej, approx. 12,000 tonnes of DrænStabil and 4,500 tonnes of asphalt were used.
Significantly cheaper than a traditional road
As of now, the municipality look forward to experience the durability of the asphalt coating. All calculations and tests show that the new type of road construction will not be more expensive over eg. 10 years, including maintenance, compared to traditional types. Thus, climate roads are in fact considerably cheaper and also far less problematic to establish than traditional types of roads, in that traditional roads will have to be supplemented with new, larger and climate-proof sewers and water collection pools, which in addition are difficult to find space for in today's urban landscape.
I am pleased that the Municipality of Aalborg, in a close co-operation with the consulting company NIRAS and the asphalt supplier NCC, are able to act so visionary in this very concrete project. This is an example of how we are moving from knowledge to action concerning the extreme weather events and cloudbursts against which, we try to protect ourselves.