The Haut-Bugey line links Bourg-en-Bresse to Bellegarde-sur-Valserine. Leaving Bourg-en-Bresse station, in the town centre, the line heads South through residential areas. It passes beneath the RN75 via an underpass built as part of the renovation of the line, then the RN79 by level crossing. A bridge carries the line over the A40 motorway to the first slopes of the Revermont in the commune of Ceyzériat. The hilly nature of the terrain required the line to take a steep and sinuous course, crossing and recrossing the route départementale several times. After the villages of Villereversure and Simandre-sur-Suran the land flattens out. The Racouse tunnel takes the line through the second ridge of the Revermont, then the Cize-Bolozon viaduct crosses the river Ain to Bolozon station. Then comes a long climb up the slopes of Mont Berthiand culminating in the Mornay tunnel after which the line runs flat and straight to Nurieux-Volognat station. The line winds through the village of Port then along the south bank of the lake of Nantua to Nantua station. A short climb through le Neyrolles along the Sylans lake to the village of Charix, then plunges down the valley of the river Semine to Bellegarde.