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A Guide To Speed Limit Signs
First introduced in 1935, speed limit signs are a familiar sight on our roads. Their meaning is obvious - but what are the rules that govern the design and placement of these signs?
In this article, we’ll look at the regulations governing speed limit signs, explore the different types of signage, and answer some common questions.
What are the regulations for speed limit signs?
Different speed limit signs and where you’ll see them
Speed limit signs: the basics
Speed limit signs are instantly recognisable to most UK drivers, with the classic design featuring a black number inside a white circle with a red border. The number represents the maximum speed for that road or zone, in miles per hour.
The exception is the National Speed Limit sign, which has a black diagonal band on a white circle.
The speed limit is determined by the road’s layout and its surroundings. These signs are essential for safety, because speed limits will change regularly throughout most journeys.
Who sets the speed limits?
Every road in the UK has a designated speed limit. The national limits for different road types are set by the government, and they also decide whether or not to apply any exceptions to these general limits.
If local authorities feel that the national speed limit is inappropriate for a particular road, they have the power to set a different limit that better reflects the road’s conditions. For example, they may decide to enforce a 20mph zone near a school, or a 60mph limit on a dual carriageway with sharp bends.
What are the regulations for speed limit signs?
Whether the speed limit has been set by the government or a local council, it’s a legal requirement that it must be clearly signed. Most speed limit signs are pole-mounted at the roadside, although wall-mounted signs are sometimes used.
For a speed limit sign to be legally binding, it must comply with the Traffic Signs Regulations and General Directions (TSRGD) 2016. This prescribes the designs and conditions of use for all traffic signs in England and Wales.
The TSRGD includes regulations for the design, size, placement, and visibility of speed limit signs.
Design
Speed limit signs must conform in appearance to the diagrams prescribed in the TSRGD. The numerals in the classic sign (diagram 670) must be in Transport Heavy alphabet and be of the correct size, and be positioned within the roundel as specified. The numerals in diagrams 672 and 673 (minimum speed limit signs) must be in the Transport Medium alphabet.
Reflectivity
All road signs in the UK must have retro-reflective surfaces so that drivers can see them in all light conditions. There are three main performance classes for reflectivity: RA1/R1 (engineering grade), RA2/R2 (high intensity), and R3B/R3C (premium).
RA2 is the standard for most permanent signage on the public highway, including most speed limit signs. The high-intensity prismatic material reflects 32% of the light from the driver’s headlights back to its source. On temporary works you may see RA1 signage.
Size
This depends on the position of the sign and whether it’s a terminal sign (to signify a change of speed limit) or a smaller “repeater” sign (to remind drivers of the current limit).
Terminal signs (diagram 670 or 671) are typically 450mm or 600mm, although their size depends on the approach speed limit rather than on the limit being signed. There are also different rules for signs at junctions. 300mm sign faces should only be used for repeater signs (although these may be larger in some cases).
Placement
Schedule 10 of the TSRGD sets out requirements for the placing of speed limit signs.
For example, terminal signs should be placed “as near as practicable” to the point where the speed limit begins or ends. It’s recommended to place one terminal sign on each side of the carriageway, especially on motorways and rural dual-carriageways.
There is no longer a specific requirement to provide repeater signs - the traffic authority may determine how many to use and where to place them. However, there are recommendations for their spacing, as well as the size.
It’s worth noting that 30mph repeater signs are only used on roads with no street lighting, while repeaters for the national speed limit are used only on roads with street lighting (apart from motorways).
Mounting
The normal mounting height for a traffic sign (measured to its lower edge) is between 900 mm and 1500 mm above the carriageway alongside it. This is to ensure that drivers can see the signs easily.
It’s important that the mounting height leaves enough clearance over a footway or cycle track, and that speed limit signs are not obscured by vegetation or other street furniture.
Ideally, there shouldn’t be any other sign on the same post as a terminal speed limit sign - but if it’s necessary, there are rules for the mounting order and the spacing between signs. Other signs (such as warnings) may appear alongside repeater signs.
Illumination
If a terminal sign on a trunk or principal road is located within 50m of an electric street lamp, it must be illuminated throughout the hours of darkness. Placing a sign on a lighting column won’t do - there has to be a separate means of illuminating the sign face directly.
Signs on unlit roads - and those on lit roads other than trunk or principal roads - must be either directly lit or reflectorised. The same applies to 20mph zones.
For more information about the regulations surrounding speed limit signs, refer to the TSRGD guidelines (Chapter 3, page 105 onwards).
Different speed limit signs and where you’ll see them
5mph and 10mph signs are reserved for places like schools or car parks where pedestrians are at close quarters at all times and the risk of a collision is at its highest. These are often used in conjunction with speed bumps to enforce the limit further.
15mph signs are used in off-highway areas such as construction sites or private drives. They are less commonly seen on UK roads.
20mph and 30mph signs are for public areas such as streets and city roads, where speed restrictions aim to reduce the risk of injury to pedestrians.
40mph speed limit signs are seen in rural or suburban areas, such as those between dual carriageways and 30mph zones.
On major roads (and motorways), the National Speed Limit sign tells you to drive at the appropriate speed for the type of road and your category of vehicle.
You will also see 50mph and 60mph signs on single carriageways, or on dual carriageways where the local authority has set a lower limit.
Motorways
Motorways have a speed limit of 70mph (for most vehicles) but numeric “70” signs are a rare sight - these only appear on motorways in Scotland and on a handful of so-called “special roads” in the UK. Special roads have individual statutes.
You won’t see a fixed speed limit sign when joining a motorway (drivers are expected to know that it’s 70mph) but there may be sections with variable speed limits indicated by gantry signage. You’ll see the National Speed Limit sign once the variable section has ended.
Minimum speed limit signs
These blue circular signs are pretty rare, indicating that drivers must maintain or exceed a certain speed. They’re used to maintain traffic flow and prevent congestion in high-risk places such as tunnels. At the end of a minimum speed limit zone, you’ll see the same sign with a red line through it.
Road markings
Some roads have the speed limit displayed on the surface. If the road marking is intended as a terminal sign, it must be accompanied by at least one upright sign. Road marking roundels may be used on their own as repeater signs, or as traffic-calming features in 20mph zones.
Wall-mounted signs
Wall-mounted speed limit signs are subject to the same regulations as other traffic signs. They are useful for areas where a pole can’t be installed, such as indoor car parks or industrial estates. These signs are typically slightly larger than post-mounted versions, and include variations to warn drivers of speed bumps.
Temporary speed limit signs
Temporary speed limits sometimes apply while roadworks are taking place. The signs for this, typically mounted on portable frames, must adhere to the guidelines in Chapter 8 of the Traffic Signs Manual - this covers the size and placement of temporary traffic signs.
Other traffic-calming options
In areas where speeding is a persistent problem, local authorities may decide to use additional measures alongside speed limit signs. These can include speed bumps, speed cushions, chicanes, and rumble strips.
Vehicle-activated signs are also popular, displaying the driver’s speed plus a message thanking them for complying or warning them to slow down. These must not be used as an alternative to fixed speed limit signs.
Closing thoughts
So, now you have an overview of the regulations surrounding speed limit signs. It’s a massive subject and we couldn’t possibly cover everything here, so we highly recommend consulting Chapter 3 of the TSRGD for in-depth guidance.
If you’re ready to buy speed limit signs, you’ll find a wide selection at Start Safety, all CE-marked and compliant with the relevant regulations. For more advice, give our friendly sales team a call!
FAQs
What does the national speed limit mean?
The national speed limit applies to all single and dual carriageways with street lights, unless there are signs showing otherwise. In built-up areas, it’s 30mph (England, Scotland, and Northern Ireland) or 20mph (Wales). On single carriageways it’s 60mph and on dual carriageways and motorways it’s 70mph (lower limits apply to certain types of vehicle).
What are yellow speed limit signs?
A yellow background is used to provide extra contrast and improve visibility (grey backgrounds are sometimes used for the same purpose). If the speed limit appears in a roundel on the sign, it is still the law. However, if it is not in a roundel, the sign is an “advisory” recommendation.
These signs may also encompass a speed camera icon or the name of a village or town. It’s neater to combine them rather than having several separate signs.
Does the speed limit start at the sign?
A terminal sign is the official point at which the indicated speed limit comes into force. If the speed limit is lower than on the previous section of road, you must be travelling at or below the new limit by the time your vehicle passes the sign. If it’s higher, you should wait until you pass the sign before accelerating.
Can I put up my own speed limit sign?
Only the government or the local authority can install speed limit signs on public roads (or where they will appear to be associated with a public road), and it’s illegal for anyone else to erect one on a public highway. You can display a “20 is Plenty” (or similar) poster or sticker on your property, but it won’t be enforceable. If you’re concerned about speeding on a particular road, you can ask your local council to consider traffic-calming measures.
How do you install a speed limit sign?
Our signs have 2 rails on the back where usually a rigid-’D’ clamp, back-to-back clamp, or universal clamp can be secured. This will depend on what you're securing the sign to and whether a sign is already fitted on the other side of the pole. For wall-mountable signs, you can use an adhesive or screw them into the wall. There are a lot of mounting options available and our staff are available to advise.
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