A UK motorist recently set off a lively debate online after claiming that “99% of drivers” don’t recognize one of the country’s most common road signs.

The sign in question is circular, white, with a thick black diagonal stripe running through it.

Despite being a standard feature on British roads and part of the mandatory driving theory test, it continues to confuse — and sometimes amuse — motorists long after they’ve passed their exams.

The sign is officially known as the national speed limit sign. Yet its meaning is far from obvious to many, and its purpose is often misunderstood in practice. On Reddit, where the discussion gained traction, users joked about its interpretation, offering tongue-in-cheek suggestions such as “national drifting zone” or “go as fast as you want.” Others admitted they were unsure of its exact function or argued that in real-world driving, its sudden appearance seems to encourage reckless overtaking and speeding. Clearly, there is a disconnect between theoretical knowledge and day-to-day road use.

To clarify, the black-and-white sign indicates that the national speed limit applies from that point onward. According to the RAC, it overrides any previously posted speed limits, such as temporary restrictions or zones with a lower threshold. However, the “national speed limit” itself is not a single number. It changes depending on the type of road and the vehicle being driven, which partly explains the confusion.

For cars and motorcycles, the rules are straightforward:

• On single carriageways, the maximum is 60 mph.

• On dual carriageways and motorways, the maximum rises to 70 mph.

For other vehicles, the limits are stricter:

• Vans and light goods vehicles are capped at 50 mph on single carriageways and 60 mph on dual carriageways.

• When towing a trailer or caravan, the same reduced limits apply.

• In built-up areas, usually identified by the presence of street lighting, the default limit remains 30 mph for all vehicles, unless signs state otherwise.

This layered system means that two drivers on the same road may be subject to different maximum speeds depending on what they are driving — one more reason why confusion persists.

Even with these rules laid out, the RAC stresses that the national speed limit is not a target. Drivers must exercise judgment and adjust their speed to conditions. Weather, visibility, traffic density, and the quality of the road surface may all require traveling well below the stated maximum. Heavy rain, ice, or fog can make driving at 60 or 70 mph dangerous, no matter what the law technically allows. In such cases, common sense and safety should always take priority.

The widespread uncertainty surrounding this sign highlights a broader issue: road education does not end once a driver passes their test. Memory fades, habits change, and road conditions evolve. Campaigners often argue that refresher courses or periodic theory updates could help address such gaps in knowledge. At the very least, discussions like this one serve as reminders to motorists that there is more to driving than simply obeying obvious speed-limit signs.

Ultimately, the national speed limit sign is not a license to drive as fast as possible. It is a flexible indicator that requires drivers to know the rules and apply them responsibly. While it may not mean “national drifting zone,” as some online jokers suggest, it does mean something far more important: the need for awareness, caution, and respect for the road.