In connection with the construction of the railway connection between Stockholm Arlanda airport and Stockholm city, an 11 km long noise barrier made of untreated European larch was built along the railway line. This provided an opportunity to implement a full-scale study comparing different untreated wood species and preservative treatments. Thus, in March 1996 ten test sections including untreated Scots pine, Norway spruce, European larch, and Scots pine with different preservative treatments were installed. The test sections have been inspected a number of times, the most recent in November 2021 after 25 years of exposure. Besides the more or less decayed top boards of untreated materials and Scanimp KF-treated all sections (above ground) inspected were in quite good condition. For the sections of untreated wood evidence of decay was observed only in smaller spots, mostly in the triangular wedge strips. These were also often subject to mechanical damages. Except for the CCA class A treated, all boards in ground contact (waste boards) had advanced decay. Preservative-treated boards with decay consisted, as far as could be observed, almost entirely of heartwood with insignificant penetration. No other sections of the noise barrier were inspected, and nothing can therefore be concluded concerning the overall performance of the European larch. Other exposure situations along the railway line, e.g. where vegetation grows close to the barrier, means a higher risk and probability for decay compared to the exposure conditions for the test sections. All sections were heavily subject to graffiti, and it was not easy to evaluate any colour changes. However, the coated Scanimp KF section as well as the CCA- and Royal-treated sections seem to have kept their original colours best. The larch had become black and its colour was far from the original light reddish colour. The trial shows that good design is crucial for the performance in above ground situations. With the present exposure, untreated materials and treated materials had performed roughly the same.

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