Fast trains act like giant pistons inside narrow tunnels

When a Japanese L0 Series Maglev train enters a tunnel at 311 miles per hour, it stops being a vehicle and starts acting like a high-speed plunger. Because the train fills nearly the entire tunnel opening, the air has nowhere to go. Instead of flowing around the sleek nose, it bunches up into a wall of high-pressure air that races ahead at the speed of sound. This creates a massive resistance that forces the train to use exponentially more power just to fight against the invisible wall it is building for itself.