When a tram brakes there is a huge volume of air getting inside the vehicle, if the windows are open. Why? I have noticed this weird phenomenon. When a tram brakes with the windows open, there is a huge volume of air entering the vehicle. Much, much more air gets in when it brakes than when it accelerates or has a constant speed. Even if it is moving very slowly, 1-2 Km/h, when it stops the volume of air is much greater than in any other situation. The volume of air does depend on the level of deceleration. If the tram brakes from a high speed there will be more air getting inside than if it brakes from a lower speed. Still, even at very low speeds the volume of air is substantial. The air current is always coming from the front to the back of the tram.
I was wondering, could this have something to do with the pressure in front/ at the back of the tram? Like, having such a square front and back, maybe it creates more air pressure in front and less in the back, and when it stops, the air moves from the front to the back. But, could this happen even at very low speeds? I noticed that when two metro trains meet in a tunnel, from opposite directions, you can feel a small brake, both when they meet and when they part away. I assume this is caused by the pressure/vacuum they create.
I don't think this is caused by a mechanism of the tram (like the brakes themselves) as there is no sound of air being released and the overall senseation is of a breeze sweeping the tram. 
Is this a known phenomenon ? 
Every time when I get home from work I notice this and it drives me crazy, so  I decided to ask you guys, maybe you can explain to me why is this happening. 
Here are two pictures of the tram:
http://metropotam.ro/mediaserver/v/q/012-19-1.jpg
http://jurnalul.ro/thumbs/big/2012/10/26/tramvaie-23-27-40-trasee-modificate-weekend-doua-linii-speciale-18431793.jpg
Thank You
 A: It's difficult to give a definite answer based on the description of the phenomenon (I've never encountered it where I live), so here are a few hypotheses that you might test.
If the air displacement is directly caused by the acceleration and deceleration, you would expect the air to flow backward during acceleration and forward during deceleration. Moreover, the flow speed would be lower than the speed involved, and air flowing at a speed of 2 km/h would not feel like a breeze.
It could be that the brake system pulls in air for cooling purposes. You commented that this is not likely because you don't hear it. Try to find out where the air leaves the tram vehicle: through the windows on the back or through some venting aperture out of direct view?
It could be that the motor or brakes at the back are not so much actively pumping air, but that there is a column of rising air near the outside, at the back, that pulls out air via the back windows as a side effect. Try standing next to the back of the tram as it arrives and see whether the hot air is there. Try closing the windows in the back.
Maybe something opens in the front of the tram just before it stops, with the explicit purpose of refreshing the air.
And of course, you could ask the driver...
A: I'd rather guess it is effect of some external factor. Maybe wind around the tram station is typical for some certain direction, or something like so.  
