New Car Speed Limiters Struggle with Accuracy, Raise Driver Concerns

Automatic speed limiters, a mandatory feature in all new cars sold in Europe and the UK since July 2024, are exhibiting significant inaccuracies, potentially leading to fines for drivers. Thatcham Research, a vehicle safety and security organization, found that the Intelligent Speed Assist (ISA) systems failed to correctly identify speed limit changes in up to one in four instances during testing on UK roads.

System Performance and Implications

Thatcham Research analyzed ISA performance in three different car models. The least accurate system, found in a budget Chinese SUV, correctly recognized the speed limit only 74.3% of the time. This level of inaccuracy raises concerns not only about potential danger if drivers become overly reliant on the technology but also about the risk of drivers receiving fines and license points due to incorrect speed limit displays.

Intelligent Speed Assist systems utilize a combination of GPS data, satellite navigation, and cameras to determine the current speed limit. When a vehicle exceeds the detected limit, the system initially alerts the driver through visual cues, audible alarms, or haptic feedback. If these warnings are disregarded, the system can automatically reduce the car's speed by restricting engine power, not by applying brakes. The system can be temporarily overridden for actions like overtaking, but EU regulations require it to be reactivated automatically each time the vehicle is started, meaning drivers who wish to disable it must do so before each journey.

Regulatory Standards and Testing

Under current EU regulations (EU 2019/2144), ISA systems must pass a 250-mile test route with varying speed limits, recognizing the correct limit for at least 90% of the distance traveled to achieve type approval. The system must also display the live speed limit within two seconds of entering a new zone. However, Thatcham Research's testing adopted a different methodology, evaluating performance at each speed limit change. Under this performance-based metric, the aforementioned Chinese SUV identified the correct speed only 74.3% of the time, indicating an incorrect limit in one in four instances of speed zone changes.

The best-performing vehicle in Thatcham's test was a BMW i5, which achieved 90.3% accuracy in identifying speed limits, still resulting in potential incorrect limit indications in one in ten cases. This contrasts with its 98.39% accuracy under the EU's measurement method.

Calls for Improved Approval Standards

Yousif Al-Ani, principal ADAS engineer at Thatcham Research, stated that inaccurate readings can diminish driver confidence in the technology. Jonathan Hewett, CEO of Thatcham Research, emphasized the need for a regulatory standard that measures system performance in real-world conditions, arguing that the safety benefits of Advanced Driver Assistance Systems (ADAS) depend on drivers trusting and keeping these technologies active.

ISA is part of a broader suite of ADAS technologies mandated for new vehicles in Europe, aimed at reducing road fatalities. The European Transport Safety Council recommended ISA, anticipating a significant reduction in collisions and casualties. The mandate for ISA compliance began with new model introductions in July 2022 and extended to all new cars sold from July 2024.