The construction sector faces the challenge of mitigating climate change with urgency. Life cycle assessment (LCA), a widely used tool to assess the climate impacts of buildings, is seldom used for bridges. Material-specific phenomena such as concrete carbonation and biogenic carbon storage are usually unaccounted for when assessing the climate impacts from infrastructure. The purpose of this article is to explore the effects these phenomena could have on climate impact assessment of road bridges and comparisons between bridge designs. For this, a case study is used of two functionally equivalent design alternatives for a small road bridge in Sweden. Dynamic LCA is used to calculate the effects of biogenic carbon storage, while the Lagerblad method and literature values are used to estimate concrete carbonation. The results show that the climate impact of the bridge is influenced by both phenomena, and that the gap between the impacts from both designs increases if the phenomena are accounted for. The outcome is influenced by the time occurrence assumed for the forest carbon uptake and the end-of-life scenario for the concrete. An equilibrium or 50/50 approach for accounting for the forest carbon uptake is proposed as a middle value compromise to handle this issue. © 2017 Informa UK Limited, trading as Taylor & Francis Group