Abstract
Roads form vast, pervasive and growing networks across the Earth, causing negative environmental impacts that spill out into a ‘road-effect zone’. Previous research has estimated the regional and global extent of these zones using arbitrary distances, ignoring the spatial distribution and distance-dependent attenuation of different forms of road environmental impact. With Great Britain as a study area, we used mapping of roads and realistic estimates of how pollution levels decay with distance to project the spatial distribution of road pollution.We found that 25% of land was less than 79 m from a road, 50% of land was less than 216 m and 75% of land was less than 527 m. Roadless areas were scarce, and confined almost exclusively to the uplands (mean elevation 391 m), with only ca 12% of land in Great Britain more than 1 km from roads and <4% of land more than 2.5 km from roads. Using light, noise, heavy metals, NO2, and particulate matter PM2.5 and PM10 as examples, we estimate that roads have a zone of influence that extends across >70% of the land area. Potentially less than 6% of land escapes any impact, resulting in nearly ubiquitously elevated pollution levels. Generalising from this, we find that, whilst the greatest levels of road pollution are relatively localised around the busiest roads, low levels of road pollution (which may be ecologically significant) are pervasive.Our findings demonstrate the importance of incorporating greater realism into road-effect zones and considering the ubiquity of road pollution in global environmental issues. We used Great Britain as a study area, but the findings likely apply to other densely populated regions at present, and to many additional regions in the future due to the predicted rapid expansion of the global road network.
Highlights
Roads form vast and pervasive networks across the Earth, with an overall estimated length of 64 million km
Our findings demonstrate the importance of incorporating greater realism into road-effect zones and considering the ubiquity of road pollution in global environmental issues
Using realistic estimates of how pollution levels decay with distance, our study suggests that, whilst the greatest levels of road pollution are relatively localised, low levels of road pollution are pervasive
Summary
Roads form vast and pervasive networks across the Earth, with an overall estimated length of 64 million km (van der Ree et al, 2015). Understanding the extent of these impacts is critical for identifying where environmental protections (e.g. from further road building), environmental mitigations (e.g. pollution reduction) and environmental enhancements (e.g. habitat creation) will most benefit the health of both people and nature It can provide insights into how the environmental impacts of roads will be affected by future changes in road use (e.g. road growth and increasing traffic volumes) and associated technologies (e.g. uptake of ultra-low emission vehicles). Previous attempts to understand the impacts of roads on the environment over large regions have generally related road proximity to specific environmental impacts, often using single thresholds for the extent of the road-effect zone (e.g. 1 km) (Forman, 2000; Ibisch et al, 2016; Psaralexi et al, 2017; Torres et al, 2016). There is a need to go beyond identifying ‘where is’ versus ‘where is not’ affected by roads, and towards understanding how the intensity of environmental impacts of roads varies across space, in terms of different types of impact
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