Life cycle assessment of large scale timber bridges: A case study from the world’s longest timber bridge design in Norway

This paper seeks to use life cycle assessment to investigate the comparative environmental impacts of two proposed bridge designs for the new Mjøsa Bridge over Lake Mjøsa in Norway. The Norwegian Public Roads Administration has designed one timber and one concrete alternative for the 1650 m 4-lane highway bridge. If the timber bridge design is chosen, it will be the longest timber bridge in the world once constructed.The main motivation for building the timber bridge is to utilize local industry and to reduce environmental impacts in road infrastructure. This study aims to determine the expected emissions from both construction designs by using life cycle assessment. Life cycle assessment studies on smaller timber bridges have been carried out in the past with favorable results towards timber designs, but no bridge of this scale has been built and therefore a more comprehensive study is required to confirm if a timber bridge of this size is a sustainable choice for transport infrastructure.The results of the study show that the timber bridge has significantly lower emissions than the concrete bridge across all impact categories included in the scope of this study. Additional environmental gains can be made from end-of-life treatment of materials. This study shows that large scale timber bridge designs should be considered for future road projects.