Intelligent speed assist systems fail to read road signs 25% of the time, research finds
A new study has found that cars are getting speed limits wrong in up to one in four sign changes...
Safety experts are calling for new testing standards for in-car speed limit assist systems, after they found that cars are displaying the wrong speed limit in as many as one in four instances.
Intelligent speed assist (ISA) is one of several advanced driver assistance systems (ADAS) that are mandatory to all new cars sold in the European Union and the UK under the former’s GSR2 safety regulations.
ISA uses built-in cameras and/or satellite navigation data to communicate the prevailing speed limit and alert the driver when it changes. Some systems will even adjust the car’s speed according to the new limit. The aim is to reduce the risk of collisions and injury by helping drivers stay within speed limits.
Under EU regulation, ISA systems must be tested over a combination of roads with a distance totalling 250 miles. The systems must recognise the correct speed limit at least 90% of the time to pass the test, and it must be able to display the limit within, at the latest, two seconds of the car passing the road sign.
However, a new study conducted by independent safety organisation Thatcham Research found inconsistencies in the way ISA systems are currently evaluated compared with how they actually perform in real-world driving.
The study evaluated ISA systems in three cars – the BMW i5, MG ZS and Tesla Model Y – using an “event-based approach”, measuring the cars on their performance at each change of speed limit rather than over distance travelled. According to Thatcham, the systems in these vehicles represent around 10% of those in new cars.
The MG ZS was the worst-performing of the three. While it achieved a 91.3% accuracy score across the distance travelled – just over the EU’s 90% threshold – it scored just 74.3% under Thatcham’s event-based accuracy testing. That means, in roughly one in four instances, the ZS’s ISA system displayed the wrong speed limit.
The best-performing vehicle, the BMW i5, achieved 98.39% accuracy across the driven distance – passing the EU’s threshold by quite a margin. However, under Thatcham’s testing, it scored 90.3%, indicating inaccuracies in around one in 10 speed limit changes.
In the case of all the vehicles tested, the ISA systems displayed speed limits that aren’t legal in the UK, including figures of 5, 10, 15 and 100mph. Thatcham Research pointed out that displaying speed limits that are not plausible can lead to increased collision risk if the ISA is linked to the car’s adaptive cruise control (ACC) system, potentially causing unwanted harsh braking or acceleration. There is also the potential that drivers will lose confidence in the technology and disable it altogether, causing its safety benefits to be lost.
Thatcham is urging regulators and industry bodies to develop the current testing framework by including event-based assessment for ISA like the testing it carried out in its study. It states this would better reflect real-world driving conditions and inspire more consumer confidence in the technology.
To improve event-based accuracy, there would need to be improvements made to the underlying safety systems fitted to the car, including camera recognition, satellite navigation data and sensor calibration.
Jonathan Hewett, CEO of Thatcham Research, said: “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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