A EXPERIMENT OF THE NOISE BARRIER WITH A VEGETATION COVER

The Finnish National Road Administration began in autumn 1995 an ex-periment to find out if vegetation planted in a noise barrier could be used in the Finnish climate for improving the visual appearance of noise barriers. The test site was located in Hameenlinna along main road number 10. The experimental noise barrier was demolished in 1999 because of poor growth of the planted vegetation. The structures and the follow up of the vegetation is described in this report. The length of the experimental noise barrier was 50 m. It consisted of the following structures: gabion wall with bushes and stonecrops. Two round towers covered with a plastic net, where perennials were planted. Water tanks were hidden in the towers. A concrete wall with steps for possible moss. A sloped wall filled with earth and covered with plastic net, where perennials were planted. A vertical wall filled with ballast and supported by a timber frame, called Permagrip. Some perennials were planted on it. A system for irrigating the plants was installed in the wall, but was never used. One main target of the experiment was to avoid maintenance of any kind. The success of the plants was observed during four summers (1996 -1999). At the beginning the plants grew slowly because of a dry summer. Even later only few species spread as designed, and even then only temporarily. They suffered from dryness when it was dry and from weeds when it was wet. Many species disappeared. Weeds spoiled the appearance of the noise barrier in the autumn and winter. Gabions filled with earth provides a better conditions for plants than other structures. Especially bushes succeeded. As a conclusion it may be stated that vegetation planted in the wall itself suffers from dryness or weeds. Instead of that, plants should be planted on the earth in front of the noise barrier, where more water is available and where roots would not become frozen so often.