Build it and they will come

WSP carried out the construction design of the Kaisantunneli – a pedestrian and bicycling tunnel passing under the railway yard at Helsinki's main railway station, as well as the underground Bicycle Parking associated with the tunnel. In addition, we were responsible for the construction design of the tunnel entrances and street areas opening to Kansalaistori square and Kaisaniemi park. The tunnel connects the city center divided by the railway yard with a pedestrian path and bicycle lane, and provides bicycle connection parking under train platforms.

Location

Helsinki, Finland

Project Status

Completed in 2024

The opening ceremony of the Kaisantunneli was held on May 4, 2024, marking the completion of the three-year construction project. The tunnel project has been described as the most challenging worksite in Finland and a project that will revolutionize transportation in the city center.

Accessibility to the city center and the railway station will significantly improve with the tunnel. It is estimated that the tunnel will have about 10,000 pedestrians and 10,000 cyclists per day at its peak usage. The bicycle parking accommodates around 1,000 bicycles.

The design of the tunnel and underground bicycle parking has been a multifaceted and challenging task, requiring a tremendous amount of specialized expertise and good cooperation. The development phase design was implemented together with WSP designers, the City of Helsinki, the contractor Destia Oy, the Finnish Transport Infrastructure Agency, and Helsinki Metropolitan Area Transport Ltd. Close cooperation continued throughout the project. Project manager Juha Viitala of Destia highlights the importance of inspections.

- Inspections were deemed absolutely essential in a challenging construction environment, and we met frequently in the field to familiarize ourselves with the worksite situation alongside the designers.

Thanks to our design partner WSP. Cooperation between the builder and designers went well in the Kaisantunneli project. Weekly design meetings ensured effective communication and coordination of the needs of different technical disciplines.

Juha Viitala Project Manager, Destia Oy

Juha Viitala Project Manager, Destia Oy

Structurally demanding design in challenging conditions

- The tunnel is 220 meters long. It passes below the groundwater level and 19 pairs of railway tracks. The biggest challenge in the design was how to construct, dig, excavate, support, and cast the tunnel without disturbing the track and passenger traffic at Finland's busiest station, explains architect, chief designer, and project manager, Matti Tapaninen.

Another challenge was to complete the project without altering the groundwater level and flows. This issue was resolved by dividing the tunnel into 14 sections, which were implemented and cast one by one. Temporary 20-meter-long steel auxiliary bridges were built for the tracks and pedestrian traffic above.

- The sections also form the expansion joints of the tunnel. The structure thickness of the tunnel's waterproof steel-reinforced concrete walls and roof is about 70 cm, and it withstands the loads of passing trains, says bridge structure designer, Antti Schwartz.

The tunnel has a curved shape, due to avoiding stairs leading to the platform, the eastern track technical connection, and underground cables. The curvature radius is as gentle as possible, 120 meters, ensuring good visibility on the fast-paced bicycle lane.

The tunnel has a connection to an old underground tunnel, which provides access to train platforms and the railway station, as well as further to the metro and trams. An accessible connection is implemented with a separate elevator, whose above-ground building also conceals the large smoke extraction and ventilation shafts of the underground facilities.

Tunnel length (m)

220

Bicycle parking size (m2)

1200

Bicycle parking capacity

1000

Bicycle parking ensures smooth connection

An underground bicycle parking area of 1,200 m² for nearly a thousand bicycles has been built in connection with the Kaisantunneli. The bicycle parking provides connection parking for cyclists under the train station, near metro and tram stops, and the city center.

Various types of bike racks, bike maintenance equipment, battery charging and storage cabinets, and a bike maintenance service point are located in the bicycle parking. Large, rounded windows in the wall between the bicycle parking and the tunnel provide views between different areas.

Access to the tunnel is adapted to the surrounding urban area

The eastern entrance of the tunnel located in Kaisaniemi park is designed to be low, open, and rounded, preserving the view towards the Parliament House. It combines two tunnels, the old platform tunnel and the new pedestrian and bicycle tunnel. A heating system connected to district heating was installed on the slope. The eastern end also includes a bicycle parking area and red oak plantings located on the slope in Kaisaniemi park.

Image: The western entrance of the tunnel opens fan-like towards the Oodi library located in Kansalaistori square, with space for city bikes, seating stairs, and individual tree plantings.

Even and refined lighting

The primary goal of the lighting design is to consider the accessibility and safety needs of the tunnel and the urban and architectural values. The lighting of the tunnel and bicycle parking is designed to be recessed into the ceiling, creating a smooth and serene appearance. The chosen light color is 3000 kelvins, a warm white.

The technical requirements of the railway and city outdoor lighting have been taken into account in the lighting fixture choices, especially at the low western entrance of the tunnel, where the end lighting is recessed into the ceiling surface among the reinforcements.

- The diagonal placement of the recesses is aligned with the location of the tracks above. The lighting dimensions and controls aim to acclimate the eye to the differences in brightness between outdoor and indoor spaces, explains lighting designer Heini Myllyoja.

The lighting in the bicycle parking is controlled based on the usage of the spaces in the evening and nighttime. In addition to general lighting, more detailed lighting is used in the lower ceiling edges, highlighting window openings, and accentuating the walls of the tunnel entrances and elevator tower.

- We wanted the curved central section of the tunnel to have a fresh and bright appearance. The edges of the lowered ceiling are illuminated, lightening the ceiling surface and creating the feel of natural light in the underground space, Heini describes.

Image: The walls of the Kaisantunneli are coated with anti-graffiti lime-colored and matt-glazed 45x90cm tiles. The upper part features accent lighting, and the lower part has a contrasting baseboard.

History of the Kaisantunneli

The connection design for the Helsinki railway yard has undergone various phases of planning, which have in part prepared for the design solutions of the Kaisantunneli and the construction design prepared by WSP. Previous phases have included general planning for the city's project decision-making. Sitowise Oy and Lindroos Architects Oy have been involved in the planning.

The decision to build the tunnel was made by the city council in 2019. General planning alternatives in 2011 included a tunnel option connected directly to the old pedestrian tunnel with a spiral ramp at the western end, which was abandoned for traffic safety reasons. Another option in 2017 was an overhead steel bridge over the railway yard, which was cheaper but posed challenges with higher elevation and ramp length.

The old pedestrian tunnel leading to the platforms was completed in 2000. However, the connection was not extended to Kansalaistori square, nor was space allocated for cycling needs in the tunnel at the beginning of the millennium. The Kaisantunneli and bicycle parking project can be seen as part of the development and change of downtown traffic, taking into account urban and environmental values. In numerous downtown plans of the last century, solutions for car traffic bridges and ramps have been proposed at the same location where the Kaisantunneli has now been implemented this millennium.