Motorists using the M4 in South Wales are being warned not to fall for a common speeding myth that could leave them facing fines, penalty points or even a driving ban.
Many drivers mistakenly believe smart motorway speed cameras are only active when variable speed limits are in place.
However, motoring specialists have stressed that motorway cameras can enforce speed limits at any time, including the national speed limit of 70mph.
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Graham Conway, from vehicle leasing firm Select Car Leasing, said a surprising number of motorists still misunderstand how speed cameras work.
Mr Conway explained: "We hear this quite often, but it's something that could potentially ruin your day if you get it wrong.
"It appears that many motorists think the speed cameras on smart motorways are only in operation when the matrix signs on the gantries show a variable speed limit, say 50mph or 60mph.
"They are aware that they need to slow down when they see this, but wrongly believe that at other times they won't get clocked breaking the speed limit, as long as they don't encounter the police.
"This simply is not right.
"Online motoring forums are full of accounts from drivers who've been caught out in such a manner.
"And the penalties for breaking the speed limit on a motorway can be severe. That's as well as being dangerous and putting lives at risk, of course."
The warning is particularly relevant for drivers on stretches of the M4 where smart motorway technology and variable speed limits are used to manage congestion, roadworks and incidents.
How do speed cameras work?
Speed cameras use radar technology or road markings to monitor a vehicle's speed and gather evidence of speeding offences.
Most modern systems are fully digital and can also monitor average speeds over longer distances.
These systems can record:
- Vehicle speed
- Time and location of the offence
- Vehicle registration
- The road's speed limit
In some cases, cameras can also capture images showing the driver and passengers.
What speed actually triggers a camera?
There is no legal rule automatically allowing motorists to exceed the speed limit.
The National Police Chiefs' Council recommends a "10% plus 2mph" threshold as guidance for enforcement discretion, but it is not a legal requirement and can vary depending on the area and circumstances.
BigWantsYourCar.com said: "The idea that you're safe doing 35mph in a 30 zone is one of the biggest myths we hear.
"Technically, you're liable for a fine the moment you go even 1mph over the limit."
The RAC also warns that drivers can be prosecuted as soon as they exceed the posted limit.
It said: "The law states that you are liable for a speeding fine as soon as you exceed the limit, so if you're doing 31mph in a 30 limit or 71mph on a motorway, you're breaking the law and could receive a fine.
"It is well worth remembering this is totally dependent on the officer who catches the speeder, and it is up to that officer whether to fine the offender or not.
"The best advice is to not speed full stop."
Other common speed camera myths
Is it true that speed vans have to be visible at all times?
There is no law requiring speed enforcement vans to remain visible.
Although enforcement officers often position themselves where they can be easily seen, they are not legally required to do so.
GoSafe Casualty Reduction Officer Gareth Thomas said: "Legally, we don't have to be visible.
"I could camouflage myself if I wanted to - but it's all about being fair, education and preventing an accident.
"Even if I parked my van and went for a walk somewhere, it would deter people from speeding right away."
Is it illegal to flash your headlights to alert motorists of a GoSafe speed van
Drivers who flash their headlights to warn others about a speed camera van could be committing an offence under Section 89 of the Police Act 1997, which makes it illegal to wilfully obstruct a constable carrying out their duties.
However, Mr Thomas acknowledged that proving such an offence can be difficult.
What is the penalty if you're caught speeding?
The minimum penalty for speeding is a £100 fine and three penalty points added to your licence.
In certain circumstances, drivers will be eligible to attend a Driver Education Course, which will incur a cost, but you will not have penalty points added to your licence.
How do you know if a speed camera caught you?
Unless you have been stopped by the police, there is no way of knowing for sure if you have been caught speeding.
You may notice a flash from a camera when you're speeding, but that doesn't necessarily mean you've been caught.
How to check if you've been caught speeding
There is also no way of checking if you've been caught speeding, according to RAC, unless you’ve been stopped at the roadside by police or receive a Notice of Intended Prosecution (NIP).
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A fine or Notice of Intended Prosecution (NIP) should arrive within 14 days of you being caught speeding.
It may take longer to arrive if the vehicle you were driving is not registered to your home address, the RAC continues.
Have you ever been caught speeding? Let us know in the poll above or in the comments below.
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