I live on the West Coast of the US and take a commuter train everyday to work about 30 miles. It’s not a high speed BART (Bay Area Rapid Transit) kind of train… it’s your “run of the mill” commuter train.
Anyway, for at leat part of the trip we travel through a series of tunnels. The tunnels aren’t all that long… the time it takes to traverse them is a minute or two at the most… but whenever we are in them it seems that most of passengers ears are effected by a change in air pressure in the train car. I can’t tell if the pressure is rising or dropping, but my ears begin to hurt just like everyone else’s. As soon as we exit the tunnel the pressure differential goes away and everything is fine again… until we reach the next tunnel.
So what is going on here? I assume the train is pushing the air in front of it along at 30 mph (my guess at the train’s speed) and when we enter the tunnel there is a low pressure wave that follows the engine and that’s what we are feeling… but that’s just a SWAG. Can anyone tell me what is really happening?