Piston relief ducts carry out the function of reducing the buildup of air pressure created by a fast moving train moving through a close fitting tunnel, by providing an escape route for the high pressure region of air forward the train. In the Eurotunnel, the ducts simply lead to the other running tunnel, leading to a system that assists both trains except for a few moments as they approach the same duct. Overall the system resuls in reduced energy requirements for trains using the tunnels. Another model created in Google SketchUp and exported to Trainz with RubyTMIX.