One of the last parts of the Nederlandse Spoorwegen (Dutch Railways) plan 'Rail 21', intended to reduce travel times and achieve a more reliable timetable by using more frequent and faster trains, is the doubling of the railway track between Boxtel and Eindhoven. These cities are situated in the south of the Netherlands.

The scope of the project complete re-design of the urban railway line, including:

• New projection of cable routings;
• Earthworks for the railway line;
• Construction of new tunnels and viaducts;
• A 2kilometres long tunnel, including an underground station in the city of Best;
• Changes of existing constructions;
• Construction of new bridges across the Wilhelmina Canal;
• Constructing new tracks and superstructure;
• Replacing existing tracks and superstructures;
• Implementation of interlocking and traffic control system;
• New power supply and overhead catenary system;
• Re-contruction of stations Beukenlaan and PSV Stadium in Eindhoven;
• Re-design of the yards at Eindhoven Central Station.

Tunnel and underground urban railway Station Best
The greatest bottleneck here is the section where the 4-track railway tunnel passes through the built-up area of the city of Best.
This section through the built-up area of Best is realised as a four track railway tunnel,  made of reinforced concrete, that is intended for railway traffic and will include an underground station with a platform on each track. The tunnel is partly under groundwater level. The entry sections are realised using a membrane structure. To allow normal train traffic on the line in current use, the first phase consists of the construction of two new tracks below surface level alongside the existing tracks. In the second phase, while train traffic used the two deep tracks from the first phase, the second section was constructed below surface level alongside the first. The tunnel section of the railway tunnel consists of two double track tunnel tubes, each with an internal width of 11.7 m at the narrowest point. The station section of the rail tunnel has a maximum internal width of 33.8 m. The internal vertical clearance above the rails is 5.75 m.

For the benefit of the construction of the tunnel, the local infrastructure (Spoorweglaan, Stationsstraat and Sportlaan) were temporarily removed and were replaced above the tunnel.
 
The Rail tunnel Best and it's underground station can be divided into five different sections along its length:

• Entry North, approximately 350 m long, realised as film structure, constructed in the dry inside a closed building trench, with the side edges of the film structure folded back to reduce the occupied space. At the deepest point, the membrane structure is approximately 10.5 m below surface level, with the rail at just over 4 metres below surface level.
• Open basin, approximately 155 m long, realised as reinforced concrete structure built in situ inside closed building trench, including approximately 70 m of the total 270 m platform length.
• Underground Station, length approximately 200 m, realised as reinforced concrete structure built in situ inside a closed building trench.
• Tunnel section, approximately 735 m long, realised as reinforced concrete structure and built inside closed building trench.
• Entry South, approximately 550 m long, similarly realised as a folded-back membrane structure, constructed in the dry inside closed building trench. At the deepest point, the membrane structure is just over 13 m below surface level, with the rails at approximately 6 metres below surface level.

The covered section, with a total length of approximately 935 m, is bordered by the two existing crossing roads, the Hoofdstraat/Oirschotseweg and the Willem de Zwijgerweg.

Above the underground station, a station building has been designed with a ticket sales office with extra facilities. Architectural design was done by ARCADIS architects.

The tunnel is provided with all necessary technical systems, such as:

• lighting;
• safety systems;
• means of communication, such as television cameras, intercoms, loudspeaker system etc.;
• power supply;
• pump installations for discharge of rain and sluice water;
• safety measures such as fire detection, fire extinguishing facilities, ventilation, escape routes etc.