This proposed high-speed line (HSL) parallels the existing Zagreb – Vinkovci line, through the Posavina region, along the middle course of the river Sava. The line is part of Pan-European Corridor X and upgrading is officially planned – but nothing on the scale proposed here.
West of Vinkovci, this proposed HSL would join the earlier proposed Drava plain high-speed line, from Maribor and Vienna (Wien). From Vinkovci two high-speed routes would continue to to Beograd (Belgrade), one along the motorway and one via Novi Sad. The new HSL would also connect to other new lines, into Bosnia: more on that later.
The existing line is 255 km long, and consists of Croatian lines M102, M103, and M105. It was not built as a single line, and was not completed until 1929. During the first and second Yugoslavia (1918-1992), it became the national rail axis, and a transit route to south-eastern Europe. Nevertheless, the line is single-track to Novska: there is a parallel line to Novska via Sisak, south of the Sava. The main Yugoslav highway, now the Croatian A3 motorway (E70), was built roughly parallel to the railway.
The line runs between the Sava and the Slavonian hills. Between the two is agricultural land, with many villages. The image below shows a typical section, near Novska. From left to right are the marshland of the Sava (liable to flooding), the motorway, the agricultural land, the railway, the old highway with settlements, and the hills.
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The terrain is flat, and much of the line consists of straight sections. However, they are separated by sometimes sharp curves. A new high-speed line can run alongside the existing line in some places, and along the motorway in others. The existing line should also be upgraded, to allow for intensification of services.
Long passenger rail lines have a problem: slow trains obstruct fast trains. If all trains stop at all stations, travel times will be too long. Express trains can overtake stopping trains at some stations, but that works best with a few trains per day. Frequent services require each train to arrive on time at the overtaking station: any delay disrupts all following trains. Adding reserve time minimises delays, but leaves trains standing at platforms for too long. The longer the line, the worse the problems.
Splitting the services is one solution: terminating trains must have their own terminal platforms or reversal tracks, or they will block through trains. The pattern of services partly determines the necessary infrastructure on the Sava valley line.
From Zagreb to Dugo Selo (21 km), there would be separate fast and slow tracks. High-speed trains would not stop at Dugo Selo, all others would: that requires a 6-track station there, or a bypass. Urban-regional services (S-Bahn) would terminate at Dugo Selo. There is no point in extending them another 18 km, to serve one more station at Ivanić-Grad: it can be served by regional and inter-regional trains.
Regional services from Zagreb, every 30 minutes, would stop at all stations after Dugo Selo, and terminate at Slavonski Brod, 190 km from Zagreb. A separate regional service would operate from Slavonski Brod to Vinkovci (65 km).
There were 21 stations and 20 halts between Dugo Selo and Vinkovci, but only four towns. Some villages are too small to justify a station, on an upgraded line. 20-25 stations are enough for this line, giving an average station spacing of around 10-12 km.
Fast inter-regional services (every 30 minutes) would use the fast tracks to Dugo Selo. They would serve only Ivanić-Grad ( 39 km from Zagreb, population 15 000), Kutina (population 15 000, 79 km from Zagreb), Nova Gradiška (population 16 000, 140 km from Zagreb), and Slavonski Brod. The inter-regional service would terminate at Vinkovci. To allow overtaking of regional services, all the remaining stations should have separate through tracks and platform tracks. Services diverging from the line would conform to this pattern of stops. (More later on the branch lines, and new lines).
The high-speed line itself will start at Dugo Selo, or possibly at the Zagreb ring motorway: it would continue all the way to Vinkovci station. Much of it would simply be built parallel to the existing line, on its southern side. At some places, the HSL can better diverge from the existing rail alignment.
On the first 45 km, the HSL could bypass Dugo Selo on the south, and Ivanić-Grad on the north. An alternative is a line along the A3 motorway, starting near the Zagreb ring. The Dugo Selo – Novska section was built in 1897 as a local line: it has many straight sections, with curves between them.
Click to enlarge: The base map is an Austro-Hungarian military map of around 1910, using some German place names.
At Kutina, the HSL can run about 300 m south of the existing station. The old line then turns away from the Sava, to Banova Jaruga station, the junction for the branch line to Pakrac. The HSL can certainly bypass this section, along the motorway: in fact the whole line can be relocated, since Banova Jaruga has only 750 inhabitants. At Lipovljani, the relocated line and the HSL would both rejoin the existing alignment. (With about 3 km of extra track east of Kutina station, the Pakrac branch can be kept operationally separate from the main line, and upgraded as a regional line from Kutina).
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Near Kutina, a new line across the Sava from Sisak would join the HSL, and the main line. A similar link is officially planned, but from Sunja to Novska. Both variants allow the Sisak line to duplicate the Sava main line, as a route out of Zagreb. (It is used in this way already, but the L-shaped route Sisak – Novska is inconvenient). With a new cross-Sava link, Novska would lose its role as a junction station, except for a local line to Dubica.
The HSL would continue alongside the main line, to Okučani. On this section, a new line to Banja Luka can diverge south, crossing the Sava at Gradiška, formerly Bosanska Gradiška. (This line was already planned in the first Yugoslavia, before the Second World War).
From Okučani to Zapolje, the HSL can follow the motorway, bypassing Nova Gradiška. East of Nova Gradiška, the old alignment is generally better (straighter), and suitable for a parallel HSL.
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A short bypass at Nova Kapela would avoid two curves, and the junction station (lines to Požega and Našice). This junction would also disappear, with the construction of a new tunnel between Nova Gradiška and Požega. The junction station would then be Nova Gradiška itself, a more logical arrangement. On the main line, another short new section is needed, to avoid a sharp curve at Sibinj.
Between Nova Kapela and Slavonski Brod, a new cut-off line can diverge toward Derventa and Doboj. This line would be used by high-speed trains from the HSL, and inter-regional trains from the upgraded main line.
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At Slavonski Brod, the motorway passes through the built-up area. So does the rail line, but it is straight. The best option here is to widen the existing alignment, with a tunnel for the HSL under the station zone. Slavonski Brod (population 62 000), is a the largest urban centre on the line. This is a traditional crossing point on the Sava, and the urban area extends across the river. That part is now in the Republika Srpska, and it is called Srpski Brod by Serbs, and Bosanski Brod by Bosnians.
Brod was the junction for the narrow-gauge line to Sarajevo, in Austro-Hungarian times, and is a possible junction with a regional line on a similar alignment: more on that later.
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East of Slavonski Brod, the rail line turns away from the Sava, toward Vinkovci. This is an almost straight line across an open plain, and the HSL can simply follow the existing 65-km alignment. About 20 km west of Vinkovci, the Drava plain HSL would join the HSL from Zagreb.
On the main line, the existing junction station at Strizivojna-Vrpolje would lose most of it functions. The Drava plain HSL would serve Djakovo, and a new cut-off line would link Vinkovci directly to Šamac (Slavonski and Bosanski Šamac). The old line would be retained for freight, and possibly a regional service Osijek – Djakovo – Šamac.
Vinkovci is not a large city (33 000 inhabitants), but it is a railway junction, and would retain that function, for the proposed high-speed lines.
The connecting HSL, from Vinkovci to Belgrade, is not described here. With a new alignment along the motorway, it would be about 150 km long. (The alternative HSL route via Novi Sad is not much longer, about 165 km).
The total route from Zagreb to Belgrade would be about 400 km long, with about 95% on new alignment. There are no topographic obstacles on the route: the line crosses the Sava once, in sight of Belgrade station. A line speed of 300-350 km/h is therefore feasible, and a journey time of under 2 hours, with one stop at Vinkovci.