Proposals for a high-speed line between Novi Sad and Belgrade were posted here several years ago, when official plans were still incomplete. By now, the project is nearing completion, so there is no point in proposing an alternative alignment. Most of it follows the old line anyway. The official project is less ambitious than proposed here, with lower capacity and speeds, but still a significant improvement by Serbian standards. The line was always intended as part of a longer Budapest – Belgrade route, and work has started on the rest of that route, slowly. The line in Belgrade itself still needs improvement, and the new central station is still unfinished, despite decades of work.
There are possible alternative routes between Budapest and Novi Sad, but not between Novi Sad and Belgrade. Both cities are located at strategic river crossings, and the geography determined the alignment of the railway line in 1883.
Novi Sad is located north of the Fruška Gora mountain range. The range runs east-west, it is about 80 km long, and the Danube flows east-west to avoid it. The range has a ‘promontory’ on the northern side, and the Danube also bends around this promontory. Exactly at its northern point is the fortress of Petrovaradin, and on the opposite bank is the modern city of Novi Sad. The line from Budapest crosses the Danube here.
Originally the line used the shortest river crossing, and ran under the fortress in tunnel. From there, a straight line to Belgrade would require an additional tunnel under the Fruška Gora range, so the line turned south-east, to run alongside the Danube. The Novi Sad station, and the Danube rail bridge, were later moved further east, so the line no longer needs ridge tunnels. The old line had another tunnel further south, at Čortanovci. There, the line turns away from the river, and climbs up to the plateau south of the Fruška Gora. From there, it is almost a straight line to Zemun, at the edge of the Belgrade agglomeration.
The climb from the Danube at Čortanovci was the worst section of the old line, and it has been completely replaced, by a new viaduct/tunnel combination. The bridge at Novi Sad (Žeželjev Most) had been replaced earlier, after NATO bombing in 1999. South of Čortanovci, no major work was needed – just track renewal, and realignment of some curves. However, the most that Serbia can afford was a mixed-traffic double-track railway, designed for 200 km/h, at least on the middle section. The capacity is insufficient for true demand at a European level, and in some parts of Europe new high-speed lines are faster – 300 km/h.
The most significant realignment on the new line is through the Čortanovci tunnel, and on to Beška. The two images below show the variants proposed here earlier, and the line as built.
The earlier post also proposed a new tunnel from Zemun into western Belgrade (Novi Beograd). The line drops 15 m here, from the plateau to the Danube/Sava flood plains, and technically, a new tunnel is no problem, so it can be added later. However, the earlier proposal also assumed, that the HSL would terminate near the old Belgrade central station. That station has now been closed, and the site cleared for redevelopment. The only option is the badly-designed new central station at Prokop, Beograd Centar. It was planned decades ago, for internal Yugoslav train services, not for European high-speed networks.
In theory, Belgrade is the logical interchange station, between Central Europe and the Balkan Peninsula. That is irrelevant at present, because services south of Belgrade are so bad – infrequent trains, on low-speed single-track lines. A first step is the upgrading of the Belgrade to Niš line for 200 km/h, which is at the planning stage. But even if there were high-speed lines to Belgrade from all directions, Beograd Centar in its present form would be inadequate. That is a good reason to consider new bypass lines, such as this northern bypass proposed here earlier, from Batajnica to Smederevo.
That would not, however, solve the problem for trains into Belgrade itself. The approach lines to Beograd Centar are of low quality, and shared with local and regional services. There is no space to reverse trains, or store and service them, even for short periods. It might be possible to build additional terminal platforms on the north side of the station. That would also require extra approach tracks, including an additional bridge over the Sava.
And in theory, the low-grade lines into Beograd Centar could all be replaced. The existing tunnels could be duplicated, with additional fast tracks, and the older tunnels reserved for urban and regional services. Similarly, the bridge over Sava could be duplicated, and the life-expired Danube bridge replaced, by a new four-track version. The remaining surface approaches, inside the urban area, could be four-tracked – with some limited demolition. However, even with 100% adequate approach tracks, Beograd Centar would still be badly located, and have insufficient capacity.