Thatcham Research has published findings from its real-world testing that highlight a gap in how intelligent speed assist (ISA) systems are currently evaluated for approval in the UK and Europe.
ISA, which uses camera and GPS data to read speed limit signs and communicate the prevailing limit to the driver, became mandatory on new vehicles sold in the UK and European Union from July 2024. The technology has the potential to reduce road casualties by helping drivers remain within posted speed limits. However, Thatcham Research’s findings suggest the current regulatory framework can leave gaps in how performance is captured, which may reduce driver confidence and lead some to disengage the system.
A regulatory gap in real-world measurement
Under current EU regulation, ISA systems are assessed based on accuracy over distance travelled. While this provides a useful baseline, it can overlook performance at key moments, such as when speed limits change.
Thatcham Research’s event-based approach measures accuracy at each of these change points. When applied in real-world conditions across three vehicles, this methodology highlighted a different level of performance compared with the distance-based standard.
The worst performing vehicle in real-world testing scored 91.3% accuracy across the driven distance. When assessed on an event-based metric, the system was 74.3% accurate. This means that for roughly 1 in 4 events, ISA is displaying the wrong speed limit, which is “below the level of performance for most drivers to accept and trust ISA”, Thatcham Research said.
The best-performing vehicle in real-world testing scored 98.39% accuracy across the driven distance, which implies a “near-perfect system”. This same vehicle’s event-based accuracy was 90.3% which demonstrates that with roughly 1 in 10 events being incorrect, even systems that perform comparatively well on UK roads are still not good enough for widespread acceptance. A lack of widespread acceptance of ISA is a major barrier to improving road safety.
Consequences of inaccuracy
When ISA misreads speed limits, it can lead to unexpected or inconsistent system responses. Over time, this risks reducing driver confidence in the technology, which is critical to achieving its intended safety benefits.
In the case of all vehicles, ISA displayed speed limits that are not legal in the UK. Multiple instances of 5mph, 10mph, 15mph and 100mph displayed speed limits were observed. Displaying implausible speed limits erodes driver trust and can increase collision risk when linked to the vehicle’s ACC (adaptive cruise control) system, which can cause unwanted harsh braking or acceleration.
Yousif Al-Ani, principal ADAS engineer, Thatcham Research, commented, “Systems should be aligned with the defined speed limit parameters for each market. Where readings fall outside those recognised limits, they should be filtered to avoid unintended responses. Presenting a driver with readings that fall outside recognised limits can erode confidence in the technology, and that is the trend we are seeing across the vehicles we assess.”
Thatcham Research believes the consequences of repeated inaccuracies are clear, with drivers losing confidence in ISA and switching it off. For a technology intended to improve road safety, this risks its intended benefits not being fully realised. If drivers routinely disengage ISA, the safety benefits of the legislation are reduced.
Jonathan Hewett, CEO, Thatcham Research, added, “ADAS technologies represent one of the most significant opportunities we have to improve road safety, but that opportunity is only realised if the systems work correctly and earn the confidence of the people using them. ISA is a case in point, the intent behind the legislation is sound, helping drivers stay within speed limits saves lives. But a system that misreads limits, intervenes unexpectedly or presents drivers with speed data that bears no relation to the road they are on does not assist them. It frustrates and distracts them, and they turn it off.
“The automotive industry has the capability to deliver ISA that is accurate, consistent and genuinely useful. What is needed now is a regulatory standard that demands exactly that – one that measures performance at the moments that matter, rather than allowing systems to pass approval while failing drivers in real-world conditions. Getting this right is not optional. The safety case for ADAS depends on drivers trusting these technologies enough to keep them switched on. We will continue to assess these systems and feed it into the safety pillar of our new Vehicle Risk Rating system for insurers.”
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