Global expansion of the ecological impact of extra-urban road traffic

Abstract Road traffic outside of cities (that is, extra-urban road traffic) contributes to ecological and environmental degradation, but the global extent of the ecological impact of extra-urban road traffic is unknown. Using global time-series data on traffic volumes, we generated high-resolution traffic exposure maps that enabled us to estimate road effect zones in which ecological and environmental conditions are likely to be influenced by road traffic. We estimate that the extent of the global terrestrial land influenced by moderate to very high extra-urban road traffic increased by 53% since 1975, reaching 239 million hectares in 2015. Large extents of Europe and North America have been impacted by road traffic since 1975, while the impacted area in large parts of Asia grew rapidly. Alarmingly, 63% of key biodiversity areas were impacted by moderate to very high traffic, with the expansion of road effect zones in these areas outpacing regional rates. Of all land uses, agricultural land was most affected by road traffic. As extra-urban road effect zones are considerably more extensive than urban areas, the ecological and environmental impacts of road traffic are of global concern.