Tidal flow lane control
Lane closed ahead; you should move to the next lane on the left as soon as traffic conditions allow
What it means
The white diagonal arrow warns that your lane closes further on and points you to the next lane on the left. It gives you room to plan, so use it: mirrors, signal, check your blind spot and move over while there is still a gap, rather than at the closure itself.
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Other tidal flow lane control
Sign images: Department for Transport, © Crown copyright. Used under the Open Government Licence v3.0.