REDFLEXhadecs3 - or HADECS 3, short for Highway Agency Digital Enforcement Camera System 3 - is a fixed-point speed camera used to enforce variable speed limits on the UK's smart motorways. Unlike average speed cameras such as SPECS or VECTOR, HADECS 3 measures the instantaneous speed of a vehicle at a single point. What makes it distinctive is that it automatically adjusts its enforcement threshold in real time to match whatever speed limit is currently displayed on the overhead gantry signs above the carriageway.
The first HADECS 3 system went live on the M25 motorway between junctions 5 and 6/7 in Kent on 22nd October 2014, following Home Office approval. In just the first five weeks of operation, 668 motorists were caught speeding - many of whom were unaware the camera was there, leading both drivers and the media to quickly label it a 'stealth camera'. Since then, HADECS 3 has been rolled out across a number of other smart motorway schemes throughout England.
Current confirmed HADECS 3 locations include the M1 in Derbyshire, M6 in Staffordshire, M25 in Surrey, M20 in Kent, M25 in Kent, M62 in West Yorkshire and M4/M5 in Somerset.
Pictured above: Redflex HADECS 3 speed camera site circled in red. Would you spot this camera driving at 70mph?
What is a HADECS 3 speed camera?
HADECS 3 is a fully digital, radar-based speed enforcement camera designed specifically for use on smart motorways - sections of motorway that use active traffic management (ATM) to increase capacity by deploying variable speed limits and, when necessary, opening the hard shoulder as a running lane during periods of congestion.
The system is manufactured by Redflex Traffic Systems, an Australian company with offices in Southampton. HADECS 3 cameras are small and painted grey rather than yellow, making them far harder to see than the bright yellow cameras the UK public is accustomed to - hence the widespread use of the term "stealth camera" among drivers and in the press.
HADECS 3 cameras can be mounted on overhead gantries above the carriageway or on poles at the roadside. The gantry-mounted variant is capable of monitoring up to five lanes of traffic simultaneously: up to four running lanes plus a hard shoulder when it is open as a running lane. Pole-mounted variants are used at roadside positions where gantry mounting is not practical.
How does a HADECS 3 speed camera work?
HADECS 3 cameras use non-intrusive dual radar technology to detect and measure vehicle speed. Two independent radar units operate simultaneously - measuring speed, identifying the lane each vehicle occupies, and confirming the vehicle's position relative to the camera. The dual-radar configuration eliminates the anomalies that can affect single-radar systems, such as reading the wrong vehicle in an adjacent lane, and provides two independent speed measurements for each offence.
A pole-mounted external aspect verification (EAV) unit, positioned ahead of the motorway's variable message signs (VMS), continuously monitors which speed limit is being displayed on the overhead gantry. When the displayed limit changes - for example from 70mph to 50mph during congestion - the EAV system alerts the HADECS 3 cameras to update their enforcement threshold accordingly. This happens automatically and in real time, with no manual intervention required.
When a vehicle is recorded exceeding the current enforced speed limit, the offence data - including speed reading, lane identification, vehicle position, and photographic evidence - is transmitted via a secure data network to a remote evidence receiving and control unit (ERCU). At this secure facility, the offence viewing and decision system (OVDS) decrypts and processes the violation data. Where the evidence meets the threshold for prosecution, a court file is automatically prepared.
Dual radar technology also eliminates the usual radar anomalies and allows HADECS 3 to operate reliably at sites where traditional single-radar camera systems can fail, while the two radars operate entirely independently to cross-verify each speed measurement.
Pictured above: HADECS 3 cameras manufactured by Redflex.
Pictured above: HADECS 3 multi-lane speed camera on the M3 motorway.
M25 HADECS 3 speed camera - targeting the rear of passing vehicles:
Do you have a question about HADECS 3 speed cameras? You can read UK motorists' HADECS 3 questions and answers and also submit your own unanswered question via our online form. Alternatively, read UK drivers' HADECS 3 camera comments.
Why is HADECS 3 called a stealth camera?
HADECS 3 cameras acquired the "stealth camera" label almost immediately after they first went live, and for good reason. Since 2003 it has been a legal requirement for fixed speed cameras in the UK to be clearly visible - a requirement that led to virtually all cameras being painted bright yellow. HADECS 3 cameras are painted grey and are considerably smaller than conventional roadside cameras, making them very difficult to spot - particularly at motorway speeds and when mounted within the structure of an overhead gantry sign.
The contrast with a Gatso is striking. A Gatso is a large, bright yellow box on a prominent pole - visible from hundreds of metres away. A HADECS 3 unit is a small grey device, often blending into the grey metalwork of the gantry frame above the carriageway. Many drivers do not notice them until they have already passed, if they notice them at all.
HADECS 3 cameras produce no visible flash when triggered, unlike a Gatso. There is no light output, no audible signal, and no other indication to a driver that the camera has recorded their vehicle. The first notification is typically the Notice of Intended Prosecution arriving in the post.
HADECS 3 and variable speed limits
HADECS 3 cameras are installed exclusively on smart motorways - sections of motorway where active traffic management techniques are used to regulate traffic flow. Smart motorways use overhead variable message signs (VMS) on gantries above the carriageway to display variable speed limits, lane closures and other traffic information in real time.
On a typical smart motorway, the default speed limit is 70mph. When traffic conditions require it - such as during heavy congestion, an incident, or when the hard shoulder is opened as a running lane - the displayed limit can be reduced to 60mph, 50mph or 40mph. Any change in the speed limit is communicated via the overhead gantry signs. HADECS 3 cameras then automatically adjust via the EAV unit to enforce the new limit.
When no variable speed limit is in force and gantry signs show a blank or the national speed limit symbol, HADECS 3 cameras default to enforcing 70mph. This means they are active and enforcing at all times - not only when a reduced variable limit is displayed. The large majority of HADECS 3 cameras in our database are set to enforce the 70mph national motorway limit.
HADECS 3 smart motorway locations
HADECS 3 cameras have been installed at a number of smart motorway locations across England. Confirmed sites include:
- M1 in Derbyshire and South Yorkshire
- M3 in Surrey and Hampshire
- M4/M5 in Somerset
- M6 around Birmingham and Staffordshire
- M20 in Kent
- M25 junctions 5 to 6/7 in Kent
- M62 in West Yorkshire
All of these locations are smart motorways, where the combination of variable speed limits and hard-shoulder running requires a camera system capable of automatically updating to enforce the correct limit at any given time.
HADECS 3 vs Gatso: what is the difference?
Both HADECS 3 and Gatso are fixed-point instantaneous speed cameras that measure a vehicle's speed at a single moment. However, they differ significantly in design, technology and deployment.
| Feature | HADECS 3 | Gatso |
|---|---|---|
| Speed measurement | Instantaneous (fixed-point dual radar) | Instantaneous (fixed-point single radar) |
| Manufacturer | Redflex Traffic Systems | Gatsometer BV |
| Colour | Grey (stealth) | Yellow |
| Flash | No visible flash | Yes - bright rear-facing flash |
| Lane coverage | Up to 5 lanes simultaneously | Single lane |
| Variable speed limits | Yes - auto-adjusts in real time | No - enforces fixed limit only |
| Deployment | Smart motorways only | All road types |
Both camera types issue the same standard penalty if you are caught speeding: a £100 fine and 3 penalty points.
Penalties for HADECS 3 speed camera offences
Being caught by a HADECS 3 camera carries the same penalties as any other fixed speed camera offence in the UK. If you are caught speeding, you may receive:
- £100 fixed penalty fine
- 3 penalty points added to your driving licence
- An offer to attend a speed awareness course in some cases, as an alternative to points
Crucially, the relevant speed limit is whichever variable limit was being displayed on the overhead gantry at the time - not necessarily the national motorway limit of 70mph. A driver exceeding a 40mph variable limit, for instance, may be recorded travelling at nearly twice the enforced limit, with correspondingly serious consequences.
More serious offences - where the recorded speed is significantly above the displayed limit - may result in a court summons rather than a fixed penalty notice, potentially leading to higher fines or a driving ban. The Notice of Intended Prosecution (NIP) will carry the relevant code: SP10, SP20, SP30, SP40 or SP50. For more information on speeding penalties read our speeding fines guide. For official UK government guidance visit GOV.UK speeding penalties.
