It looks simple — a plain white circle with a single black diagonal stripe. Most people drive past it without a second thought. But traffic experts say this is one of the most misunderstood road signs in the world.
Drivers guess everything: “No entry?” “Danger?” “Road closed?”
But the reality is very different — and surprisingly important.
This sign marks the beginning of a National Speed Limit Zone.
That means the road’s default maximum speed now applies, even if no number is shown. On certain roads, that can be much higher than people expect.
Here’s what it really means:
- On regular two-lane roads: 60 mph
- On dual carriageways: 70 mph
- On motorways: 70 mph
- For trucks, vans, and trailers: lower limits still apply
- You must adjust for weather, visibility, and road conditions
Why does it matter?
Because thousands of drivers unknowingly speed up or slow down incorrectly here — and fines, crashes, and confusion follow.
Most people don’t learn this sign until it’s too late. Now you know exactly what it means — and why 99% still don’t.
