A Thatcham Research report shows that EU-mandatory ISA systems commit errors in up to one in four speed limit changes.
The independent organization Thatcham Research tested the systems on BMW i5, MG ZS and Tesla Model Y models. The MG ZS reached 91.3 % accuracy under the European distance-based method but only 74.3 % when changes in limits were evaluated. The BMW i5 scored 98.39 % by distance and 90.3 % by events.
The vehicles displayed non-existent limits on British roads, such as 5, 10, 15 or 100 miles per hour. These errors can cause sudden braking when the system is linked to adaptive cruise control.
Yousif Al-Ani, principal ADAS engineer at Thatcham Research, stated that systems must filter readings outside recognized limits. Jonathan Hewett, chief executive, called for updating homologation procedures to include event-based tests.
ISA systems are part of the EU General Safety Regulation and have been mandatory since July 2024 in new vehicles sold in the European Union.