Optimum route selection for Pole Zal - Khorram Abad highway using GIS and environmental consideration

Highways are one of the most important of lifelines in society. On the other hand, road constructions have unfavorable effects on the environment in each region. In spite of abundant benefits, Pole Zal-Khorram Abad highway from southwestern Iran had various geohazards and environmental impacts on this area such as landslides, land use change, and decreasing the population of fauna and flora species. The optimum route selection is a complex multi criteria problem with conflicting objectives that need balancing. For the reason, the aim of this study was to find the optimum route based on environmental considerations. For this purpose, eight effective factors were selected, including slope angle, stratigraphy, proximity to streams, proximity to faults, land use, vegetative cover, elevation, as well as protected areas. Then, the analytic hierarchy process (AHP) and fuzzy systems were applied to standardize each effective factor using Expert Choice 11 software as engineering geological, environmental and economic viewpoint. The results showed that protected area, stratigraphy, vegetative cover, and land use were the most effective factors in recently highway route selection with a weight equal to 0.166, 0.165, 0.147, and 0.123, respectively. Afterward, the suggested route was selected by the combination of the factors based on relative weight in GIS. The selected road is 15 km shorter than existent highway. Also, the recent route has less geological hazards and negative environmental impacts. Therefore, it is recommended that this method, for decreasing environmental impacts, apply to constructed and constructing highways.