Here's a brand new passenger train that was supposed to be taking people to work the next morning - I wonder if they'd consider it an improvement not being able to see out of the window. I think it takes a team of several people a day or two to clean it all up and get the train back into service.
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On goods trains it has less of an impact although it can still cover up safety and other markings that are there for a reason. Plus it inevitably means people being in goods yards where trains can move at any moment and people can end up being badly injured or worse.
I'd prefer they targeted the expensive cars parked up around Mayfair, wouldn't you?