This overhead signal shows a green arrow pointing downward, indicating that the lane beneath it is open for traffic travelling in your direction.
Tidal flow systems change lane direction depending on the time of day to manage busy traffic flow.
What this sign means
A green arrow above a lane means you may use that lane, as it has been allocated to traffic travelling your way at this time.
These signals are common on multi-lane roads and bridges where traffic volumes vary significantly by direction throughout the day.
What to do when you see it
You can safely move into or continue using the lane shown with a green arrow.
- Check the signal is a solid green arrow, not a flashing warning
- Merge into the lane in good time and signal your intentions
- Stay alert as lane directions can change at set times
- Do not assume the lane will remain open indefinitely
How this sign is tested
The theory test may present this signal alongside the red cross to test your understanding of tidal flow systems.
You may be asked to identify which lane is safe to use based on the overhead signals shown.
Common mistakes
Drivers sometimes confuse the green arrow with a general direction sign rather than a lane control signal.
Others fail to notice when the signal changes, continuing to use a lane after it has closed.
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Practise road sign questionsFrequently asked questions
What does a green arrow signal mean on a motorway lane?
It means that lane is currently open for use, often as part of a tidal flow system to manage traffic direction.
Can the green arrow change to a red cross suddenly?
Yes, tidal flow signals change according to a schedule or traffic conditions, so drivers must stay alert.
Are tidal flow lanes common in the UK?
They are used on certain bridges, tunnels and busy urban routes to manage peak traffic flow efficiently.