A circular sign with a bold red border enclosing the number '40' indicates a maximum legal speed of 40 miles per hour.
It is usually positioned on outer urban ring roads, dual carriageways passing through developed areas, and higher-capacity suburban routes.
What this sign means
Drivers must not exceed 40 mph on this section of road.
It provides a transition speed between high-speed open roads and low-speed urban streets.
- Red ring with the numeral 40.
- Mandatory legal maximum speed ceiling.
- Common on suburban bypasses and arterial corridors.
What to do when you see it
Adjust speed to 40 mph or below as you pass the sign.
Maintain appropriate separation distances (at least two seconds in dry weather) behind vehicles ahead.
How this sign is tested
Theory exams test candidates on stopping distances at 40 mph compared to lower limits.
Questions ask you to identify legal maximum speeds on different road classifications.
Common mistakes
Continuing at 50 or 60 mph when entering a 40 mph zone from a rural highway.
Failing to notice small 40 mph repeater signs along extended routes.
Test yourself on this one
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Practise road sign questionsFrequently asked questions
What is the average stopping distance at 40 mph?
The total average stopping distance at 40 mph is 36 metres (118 feet).
Are speed cameras calibrated for 40 mph zones?
Yes, speed enforcement cameras operate in 40 mph zones to enforce compliance.
Does a 40 mph limit apply to all vehicles?
Yes, unless a lower vehicle-specific limit applies (e.g., certain heavy goods vehicles).