Mountain highways have low traffic volume. However, their maintenances that require huge resources and cost are typically necessary due to the needs of social development, land conservation and natural disaster prevention and response. Recognizing the vulnerable sections of a mountainous highway and associate factors that influence their usual operation is conducive in the development of appropriate maintenances strategies and related measures.

Taking the Dasha River section of the Central Cross-Island Highway (Tai-8 Highway) as an example, this study collects historical remote sensing images for more than 60 years, processing images and interpreting highway routes, landslides and gullies at different times to identify the sections that have been rerouted or have highway structural type modifications, in order to investigate the environmental and engineering geological factors that affect the highway maintenance. Field investigation is also carried to verify the types of landslides and to evaluate rock mass conditions along the route.

Results of images interpretation reveal that, in the studied 9.4 km long mountainous highway and since the completion of the highway in 1960, four local sections have been rerouted toward hillside, even went through by tunnels, and one section has structural type modification to mitigate the influence of landslides and/or lateral erosion of the river. The locations of landslides and gullies development that are related to roads rerouted and structural type modification are all neighbouring to some sharp turns of the Dasha River and adjacent to boundaries of geological strata. The differential erosion rate caused by various lithological properties and significant changes in engineering characteristics of rock masses in the vicinity of strata boundaries account for the relatively intense lateral erosion along the river and rapid development of gullies under the impact of runoff, which are also important geological factors related with the reroutes and structural modification of highway, in association with the long-term influences of rainfalls and earthquakes.

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