Motorists are being warned to look out for a plain red circle road sign with nothing inside it - as it carries a strict rule that many drivers don't fully understand. The unusual sign, which features a red border and completely blank white centre, means no vehicles are allowed to enter.

According to the official Highway Code, the sign indicates a road that is closed to all vehicular traffic, making it illegal for motorists to continue beyond that point.

Mandy Roscoe, signage expert at Carrick Signs, says misinterpreting this simple sign can spell bad news for drivers, especially near school streets, low-emission zones, and bus-only routes.

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It's even landing motorists with hefty fines and penalty points.

She said: "Drivers see a plain red circle and think it's inactive, faded, or only applies to motor vehicles. But entering those restricted zones can mean an instant penalty notice. And, in autumn, with limited light and rain or mist, you've got even less time to spot supplementary plates showing exemptions or time windows."

The sign applies to all motor vehicles, including:

• Cars
• Motorcycles
• Vans
• Lorries

In many cases, it also applies to other vehicles such as horse-drawn carriages, although local signage will usually clarify if there are exceptions, reports the Express.

It is often used to prevent vehicles entering:

• Pedestrianised areas
• Quiet lanes
• Private roads
• Certain bridges or narrow routes

Unlike other restriction signs that display symbols - such as a car or motorbike - this one is left blank to demonstrate that the restriction applies to every vehicle, rather than just specific types. The Department for Transport employs the straightforward design so it can be identified rapidly without any confusion.

Nevertheless, drivers should be mindful of penalties for disregarding the signs. Transport for London collected £89.3million in 2023-24 from fines on red routes, a 57% increase in merely five years.

Throughout the same timeframe, on-street penalty charge notices generated £6.85million in Manchester, with more than 213,000 PCNs issued. For drivers, the repercussions are immediate: penalties usually range from £60 to £130, depending on the local authority, and enforcement is regularly conducted through ANPR or CCTV systems, making these infringements challenging to contest.

To assist motorists in avoiding unnecessary costs, Mandy suggests three simple precautions:

• Always regard a plain red circle (without pictogram) as "no vehicles at any time" unless you spot a clear exemption
• Take a moment to examine supplementary plates directly beneath the sign, as these frequently display times, permitted vehicle categories, or local exceptions
• In low lighting or harsh weather conditions, reduce speed at junctions and entrances to allow yourself additional time to read signage correctly before proceeding