# An Optimization Model for a Desert Railway Route Scheme Based on Interval Number and TOPSIS
## 3 Case Study
### Analysis of Evaluation Results  
Scheme A is located at the southern edge of the Niya National Wetland Park, neglecting the core area and buffer zone sensitive to biodiversity, and minimizing the resulting impacts on the structure, overall function, and ecosystem of the reserve. The predicted results by the proposed calculation model in this paper are consistent with the results obtained by the design experts through quantitative calculation and qualitative analysis. In terms of railway design, Scheme A is about 1.472 km shorter than Scheme C and 0.62 km longer than Scheme B. The desert railway design is attempted to avoid causing sections with serious wind-blown sand hazards. The ratio of bridges and tunnels in Scheme A is 28.59%, being the largest among the three schemes. Due to the setting of the sand crossing bridge, the project investment of Scheme A increases by USD 9.38 million and USD 15.58 million, respectively, compared with Schemes B and C, but the amounts of increase are still acceptable. The bridge will not substantially grow the area of sand-blown land, nor will it pose a serious threat to the structure and function of the wetland ecosystem along the line. Scheme C is close to the National Highway 315 and makes use of the existing access roads in the construction area. In general, the traffic conditions for railway construction, operation, and maintenance are good. In terms of wind-blown sand hazards, the three schemes will be affected by variously applied levels of wind-sand hazards. The project is located in the dry-warm temperate continental climate, with dry climate and little rain, sparse surface vegetation, and obvious land desertification. Crescent dunes have been developed in the understudied area. Strong winds and widely distributed quicksand will have adverse effects on the constructional and operational works of the railway. Since Scheme A completely bypasses the Niya National Wetland Park, it passes through a large area of moving dunes on the eastern side of Minfeng. The total length of the wind-blown sand section is about 31.952 km. Some parts of the lines in Schemes B and C are located in the protected area of the wetland park. The vegetation coverage along the railway is high and the quicksand distribution is small, so the possibility of wind-sand damage is low. The degree of sand hazard and the scale of the protection project for Scheme A are higher than those of the other two schemes. Concerning the ecological environment, Scheme A completely bypasses the wetland park, and the land occupied by the project mainly presents a small amount of forest land and shrubs, which does not affect the ecological diversity of the wetland park. Both Schemes B and C cross the Niya National Wetland Park three times, with a length of 11.875 km and 7.525 km, respectively. In addition, railway stations are reserved within the conservation area in these two schemes. The sustainability of biodiversity and water environment of the wetland park in desert areas are very weak. Scheme B crosses the wetland conservation area of the park by 4.44 km in the form of bridges and subgrade. Scheme C passes through the wetland conservation area of the wetland park by 2.095 km in the form of a subgrade. The lands occupied by the two schemes are mostly forest land, shrub forest, and river water surface. Due to the temporary and permanent lands required in the project construction, some natural vegetation, surface microorganisms, and some wild animals will inevitably be destroyed, and the number of these species in the wetland park will be reduced in a short time. The railway construction will also damage the closeness and safety of the water source of the Niya River National Wetland Park. From the point of view of the ecological environment, Scheme A is superior to Schemes B and C.  
The sandstorm environment reduces the operating conditions of the railway. When the sand damage is serious, the train speed needs to be reduced to ensure the safety of the operation.