Säntjana Kastjaam (Säntjana Central Station) is the main rail terminal in the Karolian capital Säntjana and the largest and busiest station in the country. It handles around 200,000 passengers and 1000 movements a day (excluding the underground metro) and is served by trains to all parts of the country.
By 1870, Säntjana was served by a pair of terminal stations, one of which is still extant as the Sudtjaam (served by trains approaching from the east) and the other of which (the Pohjasjaam) is now the Museum of Science and Technology for trains from the north. There was no crossing of the Vaina into Osmila at this point until 1909, which necessitated the construction of two fly junctions to allow trains from the north to reach the three possible routes. (It has never been possible for a train from a Säntjana terminus to turn south using surface tracks). The new line was served by two new stations, one on the north bank of the Vaina (the Raantajaam) and the other half way between the two junctions, which was called Säntjana Mikaelijaam (despite being some distance from the eponymous cathedral). The latter had only four platforms and was served almost entirely by S-Raud services, with four bypass tracks for non-stopping trains.
The Pohjasjaam was closed in 1951 in order to simplify movements and partly because necessary expansion was impossible due to neighbouring structures. The bridge across the Vaina was further widened and the majority of services ran into termini in Osmila. This worked well in terms of track capacity, but forced all limited-stop services to use the Sudtjaam terminus in order to serve the city centre, or else call at the inadequate Mikaelijaam if continuing into Osmila. Another two platforms were added to this station in the 1960s to aid this role.
By the 1980s passenger numbers had risen to the extent that the pressure on the existing stations was becoming unsustainable. Ideas for the development of the Mikaelijaam into a larger long-distance station had been suggested since the 1950s, but it was only now that these were seriously considered by the city authorities and the national transport authority.
Karolian architect Hama va'Pasja was responsible for the final design, a process that took almost three years with the necessary surveying and securing of public funds.
The new station was planned on a grand scale. It would contain nine through tracks on the upper level, as well as terminating platforms facing both north and south, and eight through platforms for the S-Raud and surface metro lines on the lower level. A new set of corridors and an extra platform would be constructed for Line 4 of the Metro, which was deep-level underground. The routes of the Metro 2 and 3 lines, which ran in tunnels close to the site, would also be altered to use the lower hall of the station. The most prominent feature of the new station was to be a gigantic glass-clad roof constructed of hexagonal panels, which would be largely self-supporting through the use of of lightweight alloy frame and its extremely strong shape. The only visible supports would be cantilevers at the edges and discreet bracing wires. Apart from the showpiece architecture, this design was necessary to allow for building works whilst the station was in operation, and because the support structures for the platforms would have been unable to carry the roof weight as well without becoming too big to allow for adequate platform space.
Continuing to run trains on one of busiest routes in the country whilst construction was underway presented a unique challenge to engineers. It was decided to approach the problem in three stages; first, to expand the metro station to cope with the system should it be required to replace surface trains; secondly, to terminate most S-Raud and some long-distance trains from the north at neighbouring Alafjilas Ot and Raantakorut stations, creating a temporary break in the lines which allowed only the most necessary through services to continue, and finally to complete the new build in stages so that there were never less than four platforms in service at one time.
Provisions were put in place for the passengers displaced by the works. The cross-city link tunnel to the city centre had already become operational and passengers were encouraged to use this as well as additional bus and water services. All services called at interchange stations and some were diverted through the tunnel.
In effect, the design was for the tracks bypassing the existing station to be expanded and given platforms of their own. The old station tracks remained in use during the initial part of the works; the finished design would see these re-used as terminating platforms.
Works to clear the surrounding land and demolish a relatively small number of adjacent buildings were complete by 2003. A large borehole was dug to allow a disassembled Tunnel Boring Machine to be installed underground and the new metro tunnels to be dug. The borehole was retained and later converted into a new passenger entrance for the station. There were several weekends of closures on the line to allow the existing lines to be connected to the new platforms. Once Metro 4 was back in operation, works to construct the new Metro 2/3 alignment began. These were somewhat easier due to having only to connect the new lines to the old in tunnels at one end.
Once the stability of the ground was assured, the westernmost platforms of the old station were closed and most of the old surface tracks were removed in preparation for re-alignment, along with the through tracks' viaduct. A trench around five meters below street level and around a kilometre long for the tracks was dug along with the foundations of a new main entrance at this level. At the same time, the junctions north and south of the station were remodelled to allow the flyunders needed to reach the lower level.
The lower level platforms and trackwork were in place by March 2005 along with the easternmost foundations for the roof. The initial work to build the upper level over these new platforms now began; it would be necessary to complete this before trains and passengers could use the tracks below. The design called for a series of individual viaducts for each pair of tracks/platforms, rather than a continuous floor; this would save weight, allow construction in stages and allow natural light to reach the lower levels.
One this work was complete, the new entrance was fitted out and a limited number of through services could run again via the new alignment. The old platforms were now closed and the southern approaches removed to be replaced by offices and amenities. The existing tracks were raised three meters to align with the new upper level and remodelled into terminating platforms. Finally the roof and the new eastern entrance could be completed. Now came the task of building the rest of the upper level. This would, in addition to constructing the rest of the viaducts extending beyond the station, mean relaying several kilometers of track and instilling new catenary and switches. The area inside the station was left in order to complete the roof works before track and fitting out was installed. The roof was completed on May 16th 2007 and the station basically complete in February of the following year. Passenger trials indicated only minor amendments were necessary and the new station saw full services resume following a grand opening on April 5th 2008.
The upper level platforms are numbered 1-11 and have a large set of switches to the south to allow trains to either cross the Vaina or enter the Sudtjaam approaches. Lower level platforms are numbered 20-28. The easternmost four are for the exclusive use of the Metro lines 2 and 3 as these use a different voltage and current collection system. The centre pair of tracks lie in a short tunnel to the north and south where they rejoin the upper level mainline tracks, as do the easternmost pair, however immediately south of the station these join the upper level tracks leading to the Sudtjaam terminus. The Line 4 underground platforms are numbered U1-U4 to avoid confusion and have no physical connection to any other tracks at the station.
There have been some criticisms that the station is still some distance away from the city centre, but there are other rail services using the more central cross-city link tunnel, and the Kastjaam is well served by trams and buses heading into the main city area.
The mainline and Metro 2/3 tracks are laid with Karolian broad gauge track (1514mm). The surface lines are electrified with 25kV overhead lines, whilst the Metro is third rail DC. The Line 4 tracks are laid with standard gauge and third rail power.
The main effect of the station has been to greatly increase the capacity on all routes into the city.
The upper level is used by long- and medium-distance trains, including Karolian High-Speed sets.
The lower level is used by Regio and S-Raud trains.
The station is served by the following services:
- Intercity Express HS1
- Intercity Express HS2
- Intercity Express HS3
- Intercity Express HS4
- Intercity Express HS5
- Intercity Express HS8
A short single-track heritage railway connecting the lower level to the Museum of Science and Technology is operated most days during peak season by historical locomotives of Karolia. The broad-gauge track is unelectrified and has no physical connection through the station to the main lines.