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Linear infrastructures, such as roads, highways and railways, can bring significant social and economic benefits while posing great threats to local environment and biodiversity. Although processes such as Strategic Environmental Assessment have been increasingly applied during the route planning stage of major linear infrastructures to evaluate their potential impacts, the assessment of the spatial variations in these impacts is often missing. Thus, a spatial planning tool that balances both the costs and benefits for environmental and socioeconomic aspects is needed. Here we propose a Sustainable Linear Infrastructure Route Planning Model, which incorporates the spatial assessments of potential environmental and socioeconomic impacts using factors from six aspects, which are ecosystem importance, biodiversity conservation, environmental risks, economic costs, social costs, and socioeconomic benefits. The model allows users to set weights for different factors according to specific development priorities, then produces a weighted spatial resistance map, and identifies the optimized route through least-cost path analysis. We implemented this model through a case study of the Southern Expressway Extension project in Sri Lanka to test its validity. The results showed that the route choices from our model under three hypothetical scenarios (environmental, socioeconomic and balanced) all resulted in lower negative impacts compared to the current route. The proposed model can provide decision-makers an effective tool to improve the sustainability of roads, highways and railways in the age of rapid linear infrastructure expansion across the globe. • We proposed a route planning model to assess both conservation and socioeconomic impacts. • Spatial differences in linear infrastructures' impacts are included in the route planning model. • Scenario settings are used to reflect different development and planning priorities. • Three alternative routes are identified and compared with a case study project in Sri Lanka. [ABSTRACT FROM AUTHOR]