Within the UK bridge engineering sector, fibre-reinforced polymer (FRP) decks have been increasingly used in deck replacement applications. However, study on its environmental performance is limited. This paper examines the environmental credentials of this relatively new decking system by way of a case study comparing its life cycle environmental performance – in carbon terms – with that of conventional concrete decks. In order for the findings to be more general and informative, the bridge is assumed to carry an ‘average’ volume of traffic across the highway network where it is most likely to be present. Based on the results, areas for improvement are identified in order for this decking system to be more environmentally competitive. Uncertainties and limitations of the results are also discussed.