Limit questions are solved by identifying exactly what is controlled. Is the number a maximum, a minimum, advice for a hazard, or information about enforcement? Is it about speed, overall height, overall width, or gross weight? Only then compare the sign with the road, vehicle class, and current condition.
Read the whole control
A large speed roundel at the boundary normally begins a limit; smaller copies repeat the same continuing limit. When a variable restriction ends and no new number is displayed, move to the national limit that applies to both that road and that vehicle class. Do not carry an earlier temporary number forward. Location also matters: on a lit non-motorway road in Wales, the normal unsigned default differs from the general lit-road default used in England and Scotland. A specific displayed limit still takes precedence.
| Control | Decision |
|---|---|
| Red-ringed speed number | Do not exceed the displayed maximum |
| Blue minimum-speed number | Maintain at least the displayed speed unless that would be unsafe or impracticable |
| Speed beneath a bend warning | Treat it as approach advice unless a regulatory roundel also creates a limit |
| Camera symbol | Recognise enforcement information; look elsewhere for the applicable number |
| Dimension or weight roundel | Compare the stated measure with the whole vehicle or combination |
At bridges, distinguish a warning about available headroom from a red-ringed prohibition. Low bridges are normally signed when clearance is below sixteen feet six inches, about five metres. On the bridge face, chord markings mark the boundaries between areas of different available headroom. Separate road markings on the carriageway guide high vehicles through the highest part of the arch. A lower vehicle may cross those carriageway markings and keep farther left only when its height permits and safe passage is possible. Width applies to the overall vehicle or combination, not just a load or a particular body type. A lower plate can create a narrow exemption, such as one for an empty vehicle; it does not raise the displayed gross-weight figure for a loaded vehicle.
Common misreads
- Using thirty miles per hour as the unsigned lit-road default everywhere in Great Britain. Check whether the road is in Wales, England, or Scotland before choosing the default.
- Thinking a smaller repeater cancels or restarts the number. It reminds you that the limit begun at the larger boundary sign continues.
- Keeping the last variable number after its end sign. Return to the national limit for the road and vehicle class unless another control is shown.
- Using four metres as the normal low-bridge signing threshold. The stated threshold is roughly five metres, or sixteen feet six inches.
- Applying a width restriction only to an articulated vehicle or only to its load. Compare the displayed width with the complete vehicle or combination.
- Reading an empty-vehicle exemption as permission for a loaded vehicle with an empty trailer, or reading a camera symbol as a new numerical limit.
Try it
A blue circular sign sets a minimum speed of 30 mph. When may a driver travel below that minimum?
- Whenever the driver prefers to conserve fuel
- Only while another vehicle is overtaking
- When compliance would be unsafe or impracticable
- Whenever the road has more than one lane
At a non-arch bridge, a red-ringed circular sign gives a maximum height in metric and imperial units. Your vehicle exceeds it. What does the sign mean?
- The overheight vehicle must not pass the sign.
- The vehicle may proceed at walking pace under an escort.
- The height is advisory if the bridge opening looks clear.
- Only vehicles carrying a high load are affected.
Select all that apply: which actions are consistent with the markings at a low arch bridge?
- A high vehicle should follow the left edge even when the arch is lower there.
- A high vehicle should use the marked path through the highest part of the arch.
- A low vehicle must never cross the guidance markings under any circumstance.
- A low vehicle may keep left, crossing the markings, where this enables it to pass oncoming vehicles safely.