> such doors do not work on curved platforms so signs are still useful for some really old stations that are impossible to remodel They also don't work if you'

> such doors do not work on curved platforms so signs are still useful for some really old stations that are impossible to remodel They also don't work if you've got multiple types of rolling stock with incompatible door layouts, and ideally you'll also need Automatic Train Operation – while having platform screen doors together with manual driving isn't impossible (compare the Jubilee Line in London between 1999 and 2011), it's not ideal and likely costs some capacity due to the more careful driving required for stopping accurately enough.