An independent investigation has been launched into a technical fault affecting National Highways’ variable speed cameras.

It has already led to thousands of motorists being incorrectly fined, raising fresh concerns about the reliability and governance of automated enforcement technology on England’s roads.

Over exposed

The Department for Transport (DfT) confirmed it has commissioned an external review after National Highways revealed in December that a fault had been found in variable-speed cameras across parts of the strategic road network.

The issue affected 154 cameras operating on some A roads and motorways, covering around 10% of the network.

The fault, which dates back to 2021, involved a 10-second delay between changes to variable speed limit signs and the cameras enforcing them.

As a result, some drivers were detected as speeding even though they had complied with the newly displayed limit.

National Highways has identified approximately 2,650 drivers who may have been wrongly penalised.

Depth of field

According to the DfT, National Highways instructed its camera supplier on October 17, 2025, to pause the transfer of variable speed data to police forces to prevent further incorrect prosecutions.

A Home Office-approved technical fix has now been agreed, and police forces are being supported to implement it as a priority.

Tracey Westall, a non-executive director at the DfT, has been appointed to lead the independent review.

The investigation will examine how the fault arose, how it was identified, and whether opportunities were missed to detect or prevent it earlier.

It will also scrutinise how the issue was escalated within National Highways and when key stakeholders were informed, alongside assessing governance and accountability arrangements.

The DfT stressed that the review is not intended to determine liability or assign blame, and a final report is expected within 18 weeks.

Caught in the act

The incident adds to a history of problems involving speed and traffic enforcement cameras.

In 2013, dozens of Gatso cameras across the UK were temporarily suspended after concerns emerged about incorrect calibration certificates, casting doubt on the accuracy of thousands of speeding convictions.

More recently, faults with average speed cameras on roadworks sections of the M1 and A14 led to enforcement being paused while equipment was tested and recalibrated.

In 2021, several local authorities faced criticism after bus lane and red-light cameras were found to be issuing fines despite unclear or poorly positioned signage.

In Nottingham, enforcement was halted on a key route after a camera was shown to be misaligned, capturing vehicles outside the restricted lane.

In London, Transport for London temporarily disabled a number of low-emission zone cameras after software errors led to penalty notices being issued to compliant vehicles.

Film development

Road safety campaigners say such incidents risk undermining public confidence in automated enforcement, even as cameras remain central to managing congestion and reducing casualties.

“Technology plays an important role, but transparency and robust oversight are essential if the system is to retain legitimacy,” said one transport policy analyst.

When the National Highways fault first came to light, the agency apologised to those affected and confirmed that drivers would be reimbursed and have penalty points removed where applicable.

The DfT said the review would consider whether changes to governance, supplier management or technical processes are needed to reduce the risk of similar failures in future.

As variable speed limits and digital enforcement become increasingly widespread, the outcome of the investigation is expected to shape how such systems are monitored and regulated across the network.