Tradeoffs in environmental and equity gains from job accessibility.

Increasing job accessibility is considered key to urban sustainability progress, both from an environmental and from a social perspective. However, sustainability outcomes depend on the processes contributing to accessibility trends, not just the trends themselves. Here, we ask whether sustainability benefits have followed from accessibility trends in the United States. We measure changes in accessibility from 2002 to 2014 across 909 US urban areas and decompose these changes to understand underlying infrastructure and land use processes. Our results show that job accessibility has increased across 74% of urban areas for the average resident, using both cars and transit. However, most of these accessibility gains were not achieved in ways that are inherently beneficial to environmental or social sustainability. In some urban areas, accessibility increases were conducive to reducing emissions, while in others, accessibility increases were conducive to reducing social inequities. However, accessibility increases almost never created a simultaneous social and environmental "win-win," as is often assumed. Our findings highlight how the spatial patterns of urbanization create tradeoffs between different facets of sustainability. Identifying where social objectives take precedence over environmental objectives (or vice versa) could help determine how accessibility increases can be accomplished to contribute to a more sustainable urban future.