[tichiian]

I think the reason DB introduces this kind of measures over the obviously superior first steps like "building a quieter train" is this: Walls are paid for by the state or community annoyed by the train noise. New or improved trains would be paid for by DB (a nominally private company).

Which is why stuff like "putting quieter brakes on freight trains that don't sound like fingernails on a chalk board" will take at least 20 more years if it will happen at all.