A route via the Vipava valley is one of the options under consideration, for the high-speed rail line Venezia – Trieste – Ljubljana. It would run roughly on the line Villa Opicina – Vipava village – Logatec (see the maps at the end of the Province of Gorizia Transport Study). It would not pass through Ajdovščina (the main town in the valley, population 18 000), but would have a link line to it.
The Vipava valley extends eastwards from the Isonzo / Soča river at Gorizia / Nova Gorica. The valley floor is low, but gets narrower to the east, and ends abruptly. There is a local rail line through the valley to Ajdovščina, built as the Wippachtalbahn in 1902. It did not connect to any other lines, because of the sharp rise at the head of the valley – over 300 m from Lozice (225 m), into the Postojna basin at Razdrto.
The other alignments suggested for the HSL do not pass the Vipava valley. The alignment via Divača and the Postojna basin seems the best option (for the HSL). That leaves the possibility a tunnel for regional services, from the valley to the Postojna basin. It could simply be connected to the HSL – trains would run non-stop from Ljubljana to Ajdovščina, and then continue to Nova Gorica. However, to provide better regional connections, it would be better to link it to the existing line, at Postojna station. The tunnel would be a large project, in relation to the population served – in the Vipava valley itself, and in Gorizia / Nova Gorica. Even if it was built for the newest passenger trains (allowing a gradient of 35 / 000), it would be more then 11 km long. It would be so long, that it would need to start further back along the valley (near Vipava village), to begin its climb. The tunnel would surface in the eastern part of the Postojna basin, with a new line to Postojna station, at the western end. The schematic example shows a tunnel climbing 400 m in 12 km, from 140 m to 540 m.
Given the construction of a HSL with a station at Villa Opicina, there is an alternative route to the Vipava valley. There is a 55-km line line across the Kras Plateau to Nova Gorica, built as the Karst-Bahn in 1906. The section from Villa Opicina to Nova Gorica is about 40 km long. (Trains can also reach Gorizia station, over a short connecting line). The line serves some of the villages of the Vipava valley: at Prvačina, passengers could change for trains to Ajdovščina. Note that a line from Stanjel to Postojna was once planned. That would have avoided the climb at the head of the Vipava valley, but then it would not have served the eastern valley anyway. The unavoidable choice in this case, is between an indirect route, and a complex project serving a limited population.