This proposal would realign and simplify most long-distance services to Budapest, by construction of a cross-city tunnel for Intercity and inter-regional trains. A new high-speed line to Hatvan is an essential part of the project. It is not an urban-regional line (S-Bahn, RER): see the proposal for an urban-regional metro in Budapest.
At present Budapest has three main stations, all terminal stations. Déli pályaudvar (Southern Station) is the terminus of trains from the south, but is located west of the city centre. Nyugati pályaudvar (Western Station, built 1877) is in fact located north of the city centre (the line to Vienna runs north, and then curves west at the Danube Bend). Keleti pályaudvar (Eastern Station, 1884) is the largest, and is indeed located east of the centre. See the maps of past and present rail lines in Budapest.
All three are linked by ring and tangent lines, so services may not correspond to the names: trains from Austria currently terminate at Keleti. All trains to Déli station pass through Kelenföldi pályaudvar (Kelenföld station), a large station in the south-western suburbs. Trains from the south-east pass through a suburban station at Kőbánya-Kispest. The Kelebia line, along the left bank of the Danube via Soroksár to Subotica (Serbia), has no terminal of its own. It connects to a ring line at Ferencváros station. Trains from the north-east (Miskolc) arrive at Keleti (the line turns south at Hatvan).
The proposed tunnel would link Kelenföld station directly to a new underground station at Nyugati Station. It crosses metro line 3 there, so the exact location of the line depends on detailed studies. North of Nyugati, a new high-speed line (shown in blue) would be built alongside the M3 motorway to Hatvan – avoiding the longer, curving, route via Gödöllő. Trains from the north-east would no longer run to Keleti, but to Nyugati, and on to Kelenföld. Déli station would simply be closed: metro line 2 can be extended southwards over the alignment.
The diagram shows the resulting pattern of services. There are only two routes in Budapest for long-distance trains. All trains serve either Keleti or Kelenföld en Nyugati. Trains into Keleti from the south-east (via Cegléd) connect, at Kőbánya-Kispest, with trains through the tunnel, via the existing ring line to Nyugati. (A new station at Ferihegy airport could also act as interchange point).
The tunnel would be about 5 km long, with only one station, at Nyugati. New buildings alongside the station restrict the options there, but the simplest option is probably a deep underground station, directly under the historical station building. Starting the tunnel further back, for extra depth, might increase its length to 6 km. If the line is deep enough, to clear the foundations of the buildings in the city centre (and metro lines 2 and 3), then it should be deep enough to cross the Danube.
From Kelenföld northwards, trains would use the existing line for about 2 km. The southern tunnel portal would be located south of the Villányi út (where the ground rises to the Gellert hill). The terrain is at about 125 m above sea level, and the line would drop about 50 m to cross the Danube. The northern portal would be on the existing rail line out of Nyugati station. The terrain is lower and the climb from the river crossing is less: crossing the metro lines is a bigger problem. With a 4-track station at Nyugati, the tunnel should be able to carry about 15 trains per hour. That should be sufficient for all long-distance traffic through the Budapest region, on the south-west to north-east axis. If it is not sufficient, the existing line from Kelenföld eastwards, over the Danube and through Ferencváros Station to Kőbánya-Kispest, is an alternative route for east-west interregional trains.
The historic surface station at Nyugati will still be a useful terminal for trains from the north, and from Vienna. The underground station will improve connections, since passengers avoid a metro or taxi journey to Déli or Keleti stations. The tunnel will allow new inter-regional services. It would cut journey times for several inter-regional axes, for example Nagykanizsa – Miskolc, by eliminating a terminal-to-terminal transfer in Budapest. The Győr – Szeged example shows how a new west to south-east axis can be created, using the tunnel and the link lines in the east of Budapest.
The European Union is planning to use the Kelebia line as the main route from Budapest to Belgrade, although it is single-track at present. It would form the rail route for Pan-European Corridor X, Branch B. No improvement of the existing route in Budapest itself is apparently planned. Trains would run to Keleti, and reverse there, if they were continuing to the north or west. The proposed cross-city tunnel makes a more elegant solution possible: a connecting line across Csepel Island and the Danube, approximately from Taksony to Budafok.
Trains from the Kelebia line would then serve Kelenföld en Nyugati, and could continue to Bratislava and Austria via the Danube bend line. However, see the alternative proposal for this European corridor, which would leave the Budapest – Kelebia line as an inter-regional line.