Lieråsen Tunnel is a single-tubed railway tunnel of the Drammen Line situated in Asker, Røyken and Lier in Norway. At a length of , the double track tunnel is located immediately between Asker Station and Lier Station. It is used for a mix of short- and long-haul passenger trains and freight trains.
Construction of the tunnel commenced in 1962, along with a new section of track between the tunnel and Brakerøya Station. Inadequate geological surveys ahead of construction resulted in the tunnel being built in the middle of an altered and crushed zone, delaying construction and eventually shifting the route to the southwest. The tunnel opened on 3 June 1973. In addition to providing double track, it shortened the Drammen Line by . Part of the old section of the Drammen Line became the Spikkestad Line, while the rest of line was closed. Lieråsen was the longest railway tunnel in the country until the Romerike Tunnel opened in 1999.
Specifications
The Lieråsen Tunnel is long and carries the double tracked, standard gauge Drammen Line between Asker Station and Lier Station. Running through the mountain of Lieråsen, it passes through the municipalities of Lier, Røyken and Asker. The line is electrified at . At Eriksrud, from Asker Station, there is a switch allowing trains to change track.
The tunnel has a surface profile of . The speed is limited to . This is caused by the limited profile, which creates a pressure wave when trains meet, even though the infrastructure and curvature would allow for higher speeds. Starting from the Lier end the tunnel has a slight S-curve with a radius of .
History
Planning
When the Drammen Line opened on 7 October 1872, it was long. This was originally a narrow gauge railway, but it was converted to standard gauge and electrified in 1922. The line was S-shaped between Drammen and Asker, first heading northwards to Lier, where it connected to the Lier Line. It then headed south to Røyken and then northwards again to Asker. The reason for this route was the need to limit the gradient of the line to accompany freight trains. Specifically, there is a steep slope just west of Spikkestad with a height difference of about in comparison to the lower areas below. This height difference forced the line to take the detour.
The Lieråsen Tunnel was launched as a project to cut distance and travel times between Asker and Drammen, as the Drammen Line was nearly twice the length compared to a straight line. The first proposals were developed by the Norwegian State Railways (NSB) in the early 1940s, albeit at first for a single track. During the process of double tracking the Drammen Line between Asker and Sandvika, NSB launched a proposal to build two additional sections of double track, one from Hokksund to Drammen and one from Brakerøya to Asker. For the latter two main proposals were made: one which would run from the old Lier Station to Asker and a shorter direct tunnel. The advantage of the former was the ability to still serve Lierbyen and smaller construction costs, while the latter would give a shorter overall line length. NSB called for prioritizing the Drammen–Hokksund segment if there was not funding for both.
Construction
Construction involved building a new at-grade line from Brakerøya Station to a new Lier Station and subsequently a new tunnel through Lieråsen to Asker. Lieråsen is a granite massif and was regarded to be simple area to work in. The planning was carried out with limited geological surveys. Construction started in 1963, but it was soon discovered that there were long altered zones running through the area where the tunnel was to run. Specifically, a long crushed zone was located there.
After two years the route was therefore shifted about to the southeast to avoid these zones. This resulted in a slight S-curve on the Lier end. Construction continued slowly, as nearly the entire length of the tunnel needed to be reinforced with concrete. By 1966 the cost estimate for the tunnel reached NOK 454 million, up from 64 million in 1959. Break-through of the main tunnel took place in October 1971. The price ended at NOK 175 million and construction employed up to 250 people on the site. Two workers were killed and two seriously wounded due to a blasting accident on 23 June 1972.