This high-speed line (HSL) to Banja Luka, would diverge from the proposed middle Sava high-speed line, about 120 km from Zagreb. It would follow the main road E661, which has a similar function in connecting the two cities. A parallel motorway is under construction.
There never was a rail line across the Sava river to Banja Luka. A line was already planned in the first Yugoslavia, before the Second World War. (The existing rail route from Zagreb is via Sisak, Kostajnica, and Prijedor).
Following the wars of the 1990’s, the Sava is now the border between Croatia and the Republika Srpska. (After Croatia’s accession to the EU, it will become the EU external border). With a population of about 225 000, Banja Luka is the largest city in the Republika Srpska, and now its official capital. As usual at this blog, the infrastructure proposal ignores the borders (and the political climate).
The proposed HSL is about 60 km long: it crosses the floodplain of the Sava, and the Lijevče plain, east of the Kozara hills. The last 15 km, from Laktaši to Banja Luka, are in the valley of the Vrbas. The valley is wide enough, but it is built up, constraining the alignment.
The line would begin at a junction near Okučani: the exact location depends on the pattern of services. The new line is mainly for high-speed trains from Zagreb, but it must also allow travel to intermediate stations on the Zagreb line, and eastward toward Vinkovci and Belgrade. The high-speed trains would not stop on the new line: the others would serve Gradiška on the Sava, and possibly Laktaši.
With a junction east of Okučani, high-speed trains could join the Sava high-speed line, and inter-regional trains would join the main line, stopping next at Kutina, 79 km from Zagreb. For passengers traveling east, that means a long journey back along the line.
A better option is a shuttle service from Banja Luka to Nova Gradiška (population 16 000, 140 km from Zagreb). This is a suitable transfer station, for inter-regional and regional trains, on the upgraded Sava main line. With this option, the new line from Banja Luka would fork north of the Sava, with junctions east and west of Okučani.
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From the junction, the new line would roughly parallel the main road, for 15 km to the Sava. The existing road bridge crosses directly into the centre of Gradiška, formerly Bosanska Gradiška. The town has a population of about 18 000, the municipality 60 000.
The new line could pass the western edge of the town, although that will still require some demolition. (The new motorway will pass further west). A more radical option is to relocate the existing road bridge, and use the alignment for the rail line. The station would be on a viaduct in the centre of town, which is probably no more disruptive than the present main road. The line could also be in immersed tube tunnel, parallel to the road, with a station further away from the river. Both options require demolition at the edge of the centre. Speed through the town would also be limited.
Click to enlarge: tunnel in blue, central viaduct aligned with existing road bridge in red, western alignment in yellow…
South of Gradiška, the new line would again parallel the existing main road, south though the plain. (The new motorway will run at the foot of the hills). This section is 25 km long, slowly climbing from 90m to 120m elevation. At Laktaši, the line reaches the edge of the Banja Luka agglomeration. The new line must pass east or west of Laktaši, to avoid built-up areas, and a bend in the river.
The eastern alignment would cross the Vrbas, and run through the agricultural land on the east bank. It would then cross the river again, to rejoin the straight section of the motorway in Trn. Alternatively, the line can run west of Laktaši, generally following the motorway. That requires several tunnels, under the the edge of Laktaši, and bypassing the river bend. Both variants would be about 15 km long, and both can include a station at Laktaši.
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The new line would then run alongside the motorway in Trn, past the Zaluzani aerodrome. It would then join the existing rail line from Prijedor. From there, it is 5 km to Banja Luka station: this section must be upgraded.
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The station is about 2 km from the centre. Services on the line from Prijedor would be restructured, forming an east-west route through Banja Luka, to Doboj and Tuzla. At present, the main Zagreb – Sarajevo route (two trains per day) is via Banja Luka and Doboj, but a new cutoff line via Derventa would be better: more on that later.
The proposed line is not intended as an urban rail line in Banja Luka itself: a tram system would be more appropriate. A tram line along the main road could connect to the new line, at the Laktaši station.
The proposed Sava HSL would be built for a line speed of 300 km/h. Non-stop trains from Zagreb should be able to reach Banja Luka in one hour. The shuttle service to Nova Gradiška should take about 30 minutes, even with two stops.