Train horns are operated by air this is why the other word for it is air horns.
They are only used for trains as they produce a loud noise and it can be very disturbing on the roads.
Different types are being sold in the market today; you can buy one according to where you want to install them and how loud you want the noise to be.
Because of the loud noise that they make they were initially used in emergency vehicles like ambulances and fire brigades to clear the path easily.
Trains need these because they need to make the railway guard aware that they are approaching so that they can change the rails or stop the traffic accordingly.
some people also install these in the personal vehicle just for the sake of it.
as they are readily available in the market you can buy these from the local store.
You can even buy these online.
On the internet you will find many websites selling these, you can compare prices and buy one that is preferable.
If you travel on the highway very often then, you should buy these as the sound impact can help you clear the way easily.
It may scare people but it is very helpful.
You can buy one that is not as loud as the ones installed on the trains.
While buying these online you can also buy air horn kits so that you can make adjustments from time to time.
all you have to do is make sure that the one you buy is of good quality.