Lighting the way: A global analysis of road lighting outside of urban areas

Artificial light at night (ALAN) is a growing global concern, with poorly managed lighting linked to significant health and environmental impacts. Although streetlighting in urban areas has been studied extensively, the contribution of major roads — long-distance connectors between cities — remains unstudied. In this study, we combined global geospatial datasets with VIIRS/DNB and SDGSAT-1 satellite imagery to identify and quantify lit roads outside urban areas across all countries. We then explored their relationships with socio-economic, environmental, and governance indicators. We found that the extent of lit roads outside urban areas at the country level was closely related to urban brightness, reliance on fossil fuels for development, and levels of environmental regulation and awareness. Although most countryside roads remain unlit, we identified 27 countries where more than 2 % of the roads outside urban areas were lit, accounting for up to 5.3 % of the country's total nighttime surface radiance. Most countries with illuminated rural roads included oil- and gas- producers with high GDP per capita, located in the Middle East, as well as highly urbanized, high GDP per capita nations in South East Asia. Conversely, even among wealthy countries, those with strong environmental policies and carbon-pricing mechanisms exhibit minimal countryside road illumination. This study is the first to quantify contribution of major roads outside urban areas to night-time radiance and highlights the value of nighttime sensors for advancing ALAN research.