There are a significant number of factors to consider during tunnels design in order to increase effectivity in construction, reduce schedules, and provide more appropriate cross-sections for each tunnel depending on its location, conditions of exploitation and rolling stock among others.

When a high-speed train enters in a tunnel there is an overpressure and depression in head and tail that propagates along it at the speed of sound, reflecting each time they reach the portals of the tunnel. These variations of pressure, in addition to increasing the aerodynamic drag of the train, can affect the health and comfort of passengers.

Aerodynamically speaking, it is recommended meeting health and comfort criteria. The health criterion is mandatory in accordance with the Infrastructure Technical Specification of Interoperability (TSI). The comfort criteria are variable depending on the country and are usually more restrictive in terms of sizing the free cross-section of the tunnel. During the last years, designers have developed methodologies and tools to use in calculations for achieving the best tunnel conditions for all the counterparts.

There are two consequences extracted as a result of the development of the methodologies. Firstly, the reduction of the free cross-section of the tunnel to the minimum values as required by the geometrical conditions. Secondly, being able to optimize train speed along the tunnel while complying with the aforementioned criteria, which leads to reductions in cost, improved conditions of exploitation and reduced travel times.

However, aerodynamics research cannot be limited to these studies. The future will require speed improvements and longer tunnels while keeping the same standards of safety and comfort. Currently new factors such as overpressures or depressions in tunnel installations or sonic boom effect are being investigated and included in project requirements.

In relation to this, INECO has developed a software capable of calculating the aerodynamic effects in every specific position within the tunnel, train or the installation. The software most interesting functionality is the capability of modelling and mitigate sonic boom effect.