Improving capacity south of Oslo is vital in order to increase rail transport locally and nationally – for both freight and passenger traffic. The solution is the Follo line, a new 22 km double-track
The Follo line is a new 22-kilometre double-track line from Oslo to Ski. The project encompasses the Follo line, a new station at Ski, a passing loop at Ås and a cut-off to the freight terminal of Alnabru. Oslo–Ski is currently the biggest transport project in Norway, and it will include Norway’s longest rail tunnel, consisting of twin tubes each 19 kilometres in length.
Together with the existing Østfold line, the Follo line will bring a new era for rail travel in the southeast of Norway. Four tracks into Oslo will allow more trains to run – faster and on time. Journey time for the fastest service will be cut from 22 minutes to 11. The two lines together will provide plenty of capacity for the future.
The Follo line will be the gateway to Europe, and can function as the first stage in a new high-speed line linking Norway to the Continent. The Oslo–Gothenburg–Copenhagen route is included in the Norwegian government’s high-speed study, which will be finished by 2012. Tenders for construction work on the Follo Line are expected to be out in 2013.
The Østfold line today is severely over capacity, which leads to frequent delays, with the heaviest traffic on the Oslo–Ski section. Overcrowded trains show that service levels are not keeping pace with demand. The line opened in 1879 and has since been modernised, but the alignment has remained more or less the same for over 125 years.
The railway links the communities in the region. Oslo, Akershus and Østfold have a combined population of 1.4 million. The number of people and jobs in the region is expected to increase 30 per cent by 2025. Together, the Follo line and the Østfold line can accommodate this growth.
The Oslo–Gothenburg route is Norway’s principal land transport corridor to the Continent. About 80 per cent of land-based import and export traffic passes through Østfold, largely by road at present. With the new freight cut-off, new possibilities arise with the increasing capacity for rail freight.
Passengers and the environment
Express trains will use the Follo line, freeing up capacity for more commuter services on the Østfold line. Today, about 220 trains run on the Østfold line per day. With four tracks, capacity increases to over 600 trains per day. This will make public transport a more attractive option, increasing by 70 per cent the number of rush-hour passengers arriving at Oslo central station from the region today.
Estimates show increases in at least 11,000 more public transport journeys daily. This equates to 5,800 fewer car journeys each workday and a reduction of 5,500 tonnes in annual CO2 emissions.
The expected increase in rail freight will result in 750 fewer transport trucks on the roads each workday and potentially cutting annual CO2 emissions by 30,000 tonnes.
A project on such a large scale has the potential to adversely affect people and the natural environment during construction. Thorough planning is therefore essential to keep costs, progress and environmental impact under control. The Norwegian National Rail Administration is the first organisation in Norway to produce a green budget governing the choice of materials and solutions.
Fast, safe construction
The Norwegian National Rail Administration aims to build the Follo line as quickly as possible, without harming the environment or hampering train traffic unnecessarily. A safe, watertight tunnel is crucial to the project’s progress. With maximum effort and resources on the tunnelling, construction is likely to take six years to the best of current knowledge.
Oslo central station is the hub of Norway’s passenger rail network. The Follo line will run through a densely populated region rich in cultural heritage, so there are many crucial factors to consider in the planning process.
In railway engineering terms, too, feeding two new tracks into the busiest part of the Norwegian rail system will be a complex challenge. In addition to the two new tracks for the Follo line, the connection for the existing Østfold line to Oslo S need a full rebuild, with the inbound line in a new, short stretch of tunnel.
Both drill and blast as well as tunnel boring machines are considered for the tunnel. With drill and blast operations, up to eight adits are required to achieve an acceptable construction time. The rig areas has to be sited in a densely built-up area with transport of spoil over already strongly impacted roads, partly through built-up areas. If tunnelling by TBM is chosen, there will only be a need for two or three adits, and so the impact on the surrounding areas will be less. With the TBM alternative, operation is planned from an adit approximately in the middle, using four tunnel boring machines in all. Cross passages between the tubes for every 500 metres can be blasted at the same time tunnel boring is proceeding.
North of Ski station, there is an open stretch of 1.2km for the Follo Line and rebuilding over approximately 2km for the Østfold Line. This part of the project will also include 1km of a new passing loop for freight trains.
Construction work at Ski station began in 2010. The station is to become a modern transport hub in downtown Ski and will be redeveloped in several stages. The work includes accessibility improvements for all users, expansion to six tracks, new platforms and a new service building.
The Ås passing loop consists of two 1,000-metre lengths of track on which freight trains can be held, allowing faster passenger services to overtake them. During the remodelling of Ski station, the tracks will also serve as turnbacks for local trains. The first step is to obtain the necessary zoning permits for the site.
The freight cut-off connects the Follo line tunnel with the freight lines into Alnabru freight terminal. By building the cut-off at the same time as the Follo line, The Norwegian National Rail Administration can avoid future disruption of services for construction work.
The Follo line needs the highest possible uptime, and maintenance and safety work is planned well in advance. With trains continuing to run in one tube, maintenance work can proceed without interruption in the other tube. Detailed studies have shown that twin tubes are the most reliable option for such a long tunnel. All previous double track rail tunnels in Norway are constructed with large, single tubes, but due to the heavy traffic expected on the Follo Line, this solution was not viable.
The Østfold line has an average speed of 80 km per hour. The top speed on the Follo Line will at least be 200km per hour, but even higher speeds are considered. Either slab track or ballasted track will be established. This decision will be made after the speed design is decided.
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