# Air Pressure on Trains in Tunnels
**URL:** https://boards.straightdope.com/t/air-pressure-on-trains-in-tunnels/167611
**Category:** Factual Questions
**Created:** [April 9, 2003, 6:33pm UTC](https://boards.straightdope.com/t/air-pressure-on-trains-in-tunnels/167611 "2003-04-09T18:33:06Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@dolphinboy](https://boards.straightdope.com/u/dolphinboy)
#### Post date: [April 9, 2003, 6:33pm UTC](https://boards.straightdope.com/t/air-pressure-on-trains-in-tunnels/167611/1 "2003-04-09T18:33:06Z")
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?
Steve
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [April 9, 2003, 6:51pm UTC](https://boards.straightdope.com/t/air-pressure-on-trains-in-tunnels/167611/2 "2003-04-09T18:51:41Z")
> [@](#):
>
> It is well known that a train passing through a tunnel generates pressure waves that propagate backward and forward to the portals where they are reflected. The combination of these waves with the motion of the train creates a very complex flow where the transient pressure can affect passenger comfort and cause damages on train parts. Research either on the trains or on tunnel configurations is still being carried out to alleviate the worst pressure effects.
From [this article.](http://www.vki.ac.be/research/themes/ground99/1.html)
And…
> [@](#):
>
> Wen a train enters a tunnel the air can’t simply be pushed aside, it must rush backward through the narrow space between the train and the tunnel walls to fill the space behind the train. This speeding air creates a suction on the train, just like opening the window of a speeding car can suck out maps and paper. This lowers the air pressure inside the train, which can make the passengers’ ears go pop.
From [this article.](http://amos.indiana.edu/library/scripts/tunnel.html)
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### Author:  [@sturmhauke](https://boards.straightdope.com/u/sturmhauke)
#### Post date: [April 9, 2003, 6:56pm UTC](https://boards.straightdope.com/t/air-pressure-on-trains-in-tunnels/167611/3 "2003-04-09T18:56:04Z")
The Chunnel between England and France has special valves to help stabilize the air pressure as the high-speed trains pass through.
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### Author:  [@dolphinboy](https://boards.straightdope.com/u/dolphinboy)
#### Post date: [April 9, 2003, 7:01pm UTC](https://boards.straightdope.com/t/air-pressure-on-trains-in-tunnels/167611/4 "2003-04-09T19:01:28Z")
Thanks! That was quick!
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### Author:  [@aeropl](https://boards.straightdope.com/u/aeropl)
#### Post date: [April 9, 2003, 8:25pm UTC](https://boards.straightdope.com/t/air-pressure-on-trains-in-tunnels/167611/5 "2003-04-09T20:25:15Z")
I wonder what the actual pressure difference would be? Can Dolphinboy or anyone else bring a barometer (or something similar) and take a measurement?