Special factors apply to the section in the Green Heart Tunnel. The moment that a high-speed train enters the tunnel at 300km/hour, it pushes the air in the tunnel away. This extra air pressure, also known as overpressure, cannot affect oncoming trains, because an 80 cm thick wall between the two halves of the tunnel blocks it. Additional measures were taken to prevent inconvenience inside the train.

At 24-metre intervals, the partition wall has air vents of 30 x 80 centimetres. The tunnel roof also has air vents, at the start and end and in the two airshafts and three exit shafts. Thanks to these vents, the difference in air pressure between the closed tunnel and the open air is kept to a minimum. As a result, train passengers will feel little or no pressure on their ears.

The effect of these additional measures to reduce pressure differences was examined with the aid of an advanced arithmetic model. Model experiments confirmed the found data. The arithmetic model explains what happens inside a compartment of a train if the outside pressure changes, for instance when a train enters a tunnel. The arithmetic model also shows which changes in air pressure occur in the tunnel at such a moment. In this way, the HSL Project Organization was able to come up with an optimal tunnel construction with limited effects from changes in pressure.

For information about travelling comfortably, see www.NSHispeed.nl