Hi Trudy
2 months down the line and here i am with something of an answer

A dual carriageway must have a physical barrier between the sets of oncoming traffic.
Some have only painted white lines.
Proper Dcs will have either crash barriers or wide verges edged with kerbing.
Hope that helps.

Another quirk is people who want to, say, turn right. there is a filter lane for the right but people do not enter the right side because they see hatchings. IF the hatchings are surrounded by a solid white line then that is the correct thing to do but if the hatchings are edged by broken white lines then you may enter the hatching IF it is safe to do so. many people are unaware of this even professional drivers.

On that note, i gotta go

All the best

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