Quick answer
On a smart motorway, a speed limit shown inside a red circle is mandatory. If the signs show 50, 60 or another limit, you must follow that limit until signs change, restrictions end or a different legal limit is displayed.
A Red X means the lane is closed. Move safely into an open lane and do not use the Red X lane. There may be a broken-down vehicle, collision, debris, emergency services, recovery workers or road workers ahead.
If no lower variable speed limit is shown, the usual motorway limit for cars is normally 70 mph, but you must still drive safely for traffic, weather, roadworks, lane closures and road conditions.
What is a smart motorway?
A smart motorway is a section of motorway that uses technology to monitor and manage traffic. Sensors, cameras and control systems can change speed limits, display warning messages, close lanes and help manage incidents.
Some smart motorways have used the hard shoulder as a running lane at certain times or converted it into a permanent lane. This means drivers must pay close attention to overhead signs, lane signals and emergency areas.
Variable limits
Speed limits can change depending on congestion, incidents, weather or roadworks.
Lane control
Signs can close lanes, move traffic across or warn of hazards ahead.
Emergency areas
These are places to stop in an emergency if you cannot leave the motorway safely.
What common smart motorway signs mean
Speed in a red circle
Mandatory variable speed limit. Do not exceed the displayed speed.
Red X
Lane closed. Move out safely and do not use that lane.
Amber warning signs
Hazard, queue, incident, weather warning, roadworks or obstruction ahead.
Lane arrows
Move safely in the direction shown. A lane may be closing ahead.
END
A displayed restriction has ended, but only increase speed when it is safe.
National speed limit sign
Normal national motorway limits apply unless another lower restriction is shown.
How smart motorway variable speed limits work
Variable speed limits are used to slow traffic before queues, incidents or hazards. This can reduce sudden braking and help traffic flow more safely.
- ✓If the speed is inside a red circle, it is mandatory.
- ✓Limits may change from gantry to gantry.
- ✓Do not speed up until signs show the restriction has changed or ended.
- ✓Do not assume all lanes have the same instruction if lane-specific signs are displayed.
- ✓Even below the limit, you must drive safely for weather, traffic and visibility.
Why smart motorway speed limits change
A lower limit may feel frustrating when the road looks clear, but signs can be set because of hazards further ahead. You may not see the reason immediately from your position.
Queues ahead
Limits can be lowered to reduce sudden braking at the back of traffic.
Breakdowns
A stranded vehicle may be ahead in a live lane or emergency area.
Collisions
Lower speeds can protect drivers, emergency services and recovery workers.
Debris
Objects, tyre debris or spilled loads may require lane closures.
Roadworks
Temporary layouts, workers and narrow lanes may need reduced limits.
Weather
Heavy rain, fog, spray, snow or standing water can make lower speeds necessary.
Red X lane closure rules
A Red X means the lane is closed. You must stay out of that lane because there may be a serious hazard ahead or people working in or near the carriageway.
- !Do not drive in a lane showing a Red X.
- !Move safely into an open lane as soon as you can.
- !Do not wait until the last second to move over.
- !Do not move back into the lane until signs show it has reopened.
- !Leave space for other drivers to merge safely.
- !Do not follow another driver into a closed lane just because they ignore the sign.
Ignoring a Red X is illegal and dangerous. It can put broken-down drivers, emergency services, recovery operators and road workers at serious risk.
Smart motorway cameras
Smart motorway cameras may enforce variable speed limits and lane closure rules. Treat cameras as active and follow the displayed limit. Do not assume a camera is off because there is no visible flash.
When no lower variable limit is displayed, the normal motorway speed limit may apply for cars, but cameras can still enforce speeding offences. Always drive to the signs, traffic and road conditions.
Variable limit cameras
Can enforce displayed speed limits on smart motorway sections.
Red X enforcement
Driving in a closed Red X lane can lead to enforcement and penalties.
No visible flash
Do not rely on seeing a flash. Many systems do not behave like old roadside cameras.
For more detail, read average speed cameras: how they work and speeding fine UK explained.
Can you use the hard shoulder on a smart motorway?
Do not assume the hard shoulder is available. On some smart motorway sections, it may be used as a running lane only when signs show it is open. On other sections, there may be no normal hard shoulder.
- ✓Only use a hard shoulder as a running lane if signs clearly show it is open.
- ✓Do not drive in a lane with a Red X above it.
- ✓If the hard shoulder is not open, treat it as emergency-only.
- ✓Use emergency areas only for emergencies, not rest stops or phone calls.
What to do if you break down on a smart motorway
If possible, leave the motorway at the next exit, motorway service area or another safe place. If that is not possible, try to reach an emergency area, hard shoulder where available, or another place of relative safety.
- ✓Put your hazard lights on.
- ✓Move left if it is safe to do so.
- ✓Use an emergency area if you can reach one safely.
- ✓Exit the vehicle on the left if safe and wait behind a barrier.
- ✓If you cannot leave the vehicle safely, keep your seatbelt on and call for help.
- ✓Call 999 if you are stopped in a live lane or in immediate danger.
Do not try to repair the car in a live lane. Your safety is more important than the vehicle.
Common smart motorway mistakes
- !Thinking a displayed speed limit is only advisory.
- !Driving in a Red X lane because it looks empty.
- !Speeding up too early before signs change.
- !Assuming no visible camera flash means no enforcement.
- !Using an emergency area as a rest stop.
- !Ignoring lane arrows until the last moment.
- !Following the car in front instead of reading the gantry signs.
Safe driving tips on smart motorways
- ✓Keep scanning gantry signs well ahead.
- ✓Leave a safe following distance, especially in queues.
- ✓Move out of a closing lane early and calmly.
- ✓Do not tailgate drivers who slow for displayed limits.
- ✓Adjust speed for rain, spray, darkness, fog and heavy traffic.
- ✓Know where emergency areas are as you drive.
- ✓Remember the limit is the maximum, not a target.
Helpful UK speed limit guides
Frequently asked questions
Are smart motorway limits enforceable?
Yes. Mandatory variable speed limits shown inside a red circle can be enforced by cameras.
Can smart motorway limits change quickly?
Yes. They may change because of traffic flow, incidents, lane closures, roadworks, weather or safety concerns.
What if one lane shows a Red X?
That lane is closed and must not be used until signs show it has reopened.
Does no sign mean 70 mph?
For cars, the normal motorway speed limit is usually 70 mph when no lower restriction is displayed, but always check roadworks, gantries, lane signs and conditions.
Can smart motorway cameras catch speeding?
Yes. Cameras can be used to enforce variable speed limits and other speed limits on smart motorways.
Can you use the hard shoulder on a smart motorway?
Only when signs show it is open as a running lane, or in an emergency where it is available and safe. Never assume the hard shoulder is open.
What should I do if I miss a Red X sign?
Move into an open lane safely as soon as possible. Do not continue in the closed lane.
What should I do if I break down in a live lane?
Keep your seatbelt on if you cannot leave safely, switch on hazard lights and call 999 if you are in immediate danger.