Have you ever spotted that peculiar traffic sign appearing out of nowhere — a white circle with a single black diagonal stripe — and wondered what it means? Many drivers encounter it yet remain unsure of its true purpose. This mysterious marker is none other than the national speed limit sign. Despite its simple appearance, the national speed limit sign often causes confusion on UK roads. Unlike other signs that display clear numbers, this one relies on drivers knowing the general speed limits for different types of roads and vehicles.

So, what exactly does it mean? When you see the national speed limit sign, it signals that the default speed limit for that road type applies. In other words, you must know the national rules rather than look for a specific figure on the sign itself. For cars, the national speed limit is 60 mph on single carriageways and 70 mph on dual carriageways or motorways — unless stated otherwise. However, these limits differ for vans, lorries, and vehicles towing trailers, which are restricted to lower maximum speeds.

Context matters too. The sign only applies when there are no lower limits indicated by other signs or road markings. Once you pass the black-and-white symbol, you can drive up to the national limit — but only if it’s safe and appropriate for the conditions. Weather, traffic, and visibility all play crucial roles. Even though the national limit might permit 60 or 70 mph, driving at those speeds on narrow, winding, or wet roads may still be dangerous.

It’s also worth noting that local councils sometimes impose lower limits in rural or residential areas, overriding the national rule. So, next time you see that mysterious sign, you’ll know — it’s not an invitation to speed, but a reminder to drive wisely within the nation’s general road rules.