Quantifying highway expansion impact on urban heat island effect in San Francisco bay area

The expansion of urban highways fundamentally affects the environment, yet there has been little research on how much highway creation and expansion can impact local climate and Urban Heat Island (UHI) effect. This study adopts a novel statistical approach using thermal remote sensing Land Surface Temperature (LST) and metrology data to quantify the environmental impacts of highway expansion on the UHI effect in the San Francisco Bay Area (SFBA), one of urbanized areas in the U.S. with significant highway construction over the past decades. Using accurate highway expansion project locations from California Department of Transportation (CalTrans), remotely sensed LST data were acquired from Google Earth Engine. Intensity of UHI effects were estimated for 11 highway expansions projects 1 year before and after the construction. Differing from previous UHI studies rely on broad-scale modeling or short-term interventions, this work uses a project-based pre-and-post comparison with a highway-expansion dummy variable and LST data to directly attribute localized UHI impacts. The findings of the study indicate an exacerbated UHI effect and increase in urban-rural LST difference resulting from highway expansions in the study area, correlating with changes in land use patterns. These results provide actionable insights for transportation and urban planning for mitigation strategies such as preserving vegetation, incorporating green buffers, and utilizing reflective materials for highway development. This study not only aids in understanding the non-Vehicle Miles Traveled (VMT) environmental impacts of highway expansion but also provides new analytical tools for incorporating these externalities into future urban planning and policy-making decisions. • Thermal remote sensing and Google Earth Engine is employed to model the urban thermal environment. • Statistical models are used to evaluate the impact of highway expansion on the urban heat island effect. • Results reveal that highway expansion exacerbated the urban-rural temperature disparity in San Francisco Bay area.