In this study, geographic information system (GIS)-based network analysis and analytic hierarchy process (AHP) methods were applied to the Erzincan-Trabzon segment of the Turkish high-speed railway (HSR) project. A new hybrid route, which considers both economic and environmental criteria, was created and compared with three different routes from various preconstruction studies. The route-generating analysis included the eight parameters (criteria) of slope, geology, soil quality, rivers, protected areas, roads, land cover, and lakes. The optimum route for connecting the port of Trabzon to Turkey's interior via HSR was generated. The weights for determining the route were tested for sensitivity. The study demonstrated the efficiency of GIS and AHP integration in generating optimum routes for HSR projects according to given databases. All these GIS and AHP analyses were applied automatically with our novel GIS extension for determining optimum HSR routes. The final route has preserved cultural and historical structures, environmental integrity. The new hybrid route also decreased construction costs by approximately 12%, and the least-cost-path analysis confirmed the environmental efficiency of the route.