The Bohinj railway enters the Idrijca Valley in Bača pri Modreju. Immediately behind the exit of the Bača tunnel, the train drives over the 258 (207.1?) meter-long Idrijca Viaduct, which is the longest viaduct on the entire railway track. In this part, the railway diverts from its southward direction towards the west and leads to the railway station of Sv. Lucija (Most na Soči), which is the main station for locations along the upper flow of the Soča River.
The viaduct begins with a stone section featuring seven arches, followed by a 51-meter-long iron section resting on a stone pillar, and is completed by another stone arch. On both sides of the viaduct, fortifications were built during its construction, testifying to the important military function that the Bohinj railway served.
There are 28 tunnels on the Jesenice-Nova Gorica railway with a total length of 16.1 km and 5 galleries with a total length of 565 m. The line crosses the Sava Dolinka, the Radovna, the Sava Bohinjka three times, the Bača eleven times, the Idrijca (over the 207.1-meter-long viaduct near Bača pri Modreju), and the Soča (Isonzo) twice.
If we also consider the bridges across streams, ravines, and bays, there are 65 bridges from Jesenice to Nova Gorica. To illustrate how demanding this mountain railway is, one only needs to look at the section between the stations of Hudajužna and Grahovo. On this 6.54 km long section, there are 4 tunnels totaling 1,390 m, 8 bridges with a total length of 400.46 m, 33 culverts, and 15 curves with a radius of less than 300 m; all this with a gradient between 20 and 25.8 per mille. Within just a 798 m section at kilometer "42", the track crosses the Bača four times and the road twice, passes through two short tunnels, and features 5 culverts, a ventilation device for the Bukovo tunnel, and a guardhouse.
The valley through which the railway, the road, and the Bača River pass is narrow; above it, the 1,303 m high Kojca rises on one side, and the 1,070 m high Koriška Gora on the other.
With the outbreak of World War I on the Isonzo Front, the Bohinj railway (Wocheinerbahn) line was completely taken over by the K.u.K. (Kaiserlich und Königlich: Imperial and Royal) military. This railway lifeline was used to supply the entire Tolmin bridgehead and the adjacent sections of the front. The route was mostly single-track, and the transport of necessary war material left the railroad workers no rest. South of the railway bridge at Bača pri Modreju, the railway line was within the range of Italian artillery and was later interrupted. Consequently, rail transports for several years unloaded in advance at the Hudajužna railway station. The railway station of Most na Soči (then St. Lucia) was destroyed by Italian artillery shells.
On July 18, 1915, Archduke Karl, later Emperor Karl, visited the area. The heir to the throne, together with Archduke Frederick, visited the troops in the Tolmin bridgehead. On this occasion, the battalion lined up on the large meadow in front of the railway bridge, and the future emperor inspected his men and distributed awards. This scene was repeated many times in the following years. Finally, German troops of the 14th Army marched under the bridge to replace positions in the bridgehead. From there, in October 1917, the final breakthrough on the Isonzo (the Miracle of Caporetto) began.
Sources:
Tiri in čas, K. Rustja, Železniško gospodarstvo Ljubljana, 1990, p. 29;
Austrian Emperor Karl (1887-1922), URL: vatican.va, cited June 5, 2023;
Po sledeh Soške fronte, M. Simić, MK, 1998, p. 231.