Euro NCAP Reveals Why Even 5-Star Cars Can Fail In Truck Underrun Crashes

Since the current certified underrun protection barriers failed to protect car occupants, Euro NCAP has requested European and UK regulators to upgrade their standards

Launched in 1996, Euro NCAP has played an important role in improving vehicle safety standards and saving lives. Its latest initiative focuses on a critical weakness in the underrun protection systems fitted to trucks and trailers across Europe and the UK. Euro NCAP estimates that around 400 fatalities every year are linked to rear underrun crashes involving heavy vehicles.

The latest study was initiated and supported by National Highways in the UK based on real-world collision data. Testing was carried out across laboratories in the UK, Germany and the United States, in collaboration with organisations including Germany’s ADAC, Horiba Mira, Sweden’s Trafikverket and the Insurance Institute for Highway Safety (IIHS).

Weakness of older ADAS systems revealed

To understand the risks associated with underrun crashes, Euro NCAP evaluated both advanced driver assistance systems (ADAS) and the effectiveness of current underrun protection barriers fitted to heavy goods vehicles. The tests revealed that while newer ADAS systems are far more capable, many older systems struggle to detect stationary trucks and trailers.

The evaluation covered real heavy goods vehicles including curtainside trailers, skeletal trailers and impact protection vehicles used during roadworks. Euro NCAP estimates that it could take around 15 years before most cars on the road are equipped with ADAS systems capable of reliably identifying such hazards.

Underrun crash test results

Euro NCAP also conducted physical underrun crash tests using a 5-star rated electric car with strong crash safety credentials. These tests simulate situations where both the driver and the vehicle’s ADAS fail to prevent a collision with a stationary truck or trailer. One of the tests involved a 30% passenger-side frontal offset impact at 56 km/h, a scenario commonly seen when drivers attempt a last-second evasive manoeuvre.

The results were alarming. Because the trailer’s rear structure bypassed the vehicle’s crumple zones and safety cage, it intruded directly into the passenger compartment. Euro NCAP concluded that the crash would likely have caused fatal head and neck injuries. A second 75% frontal impact test also resulted in severe intrusion, with fatal injuries considered likely for both front occupants.

Recent Tata Sierra EV demo puts Euro NCAP findings into perspective

Euro NCAP’s findings are particularly interesting in the context of Tata Motors’ recent Sierra EV safety demonstration. During the launch, Tata showcased Sierra EV automatically braking for a stationary truck using its ADAS. The SUV was then struck from behind by another truck, pushing it into the stationary truck ahead. Despite the front of the Sierra sliding partially underneath the truck, Tata demonstrated that the passenger compartment remained intact and occupants would have escaped without serious injuries.

Euro NCAP’s latest crash tests, however, show that a similar underrun-type impact can have a vastly different outcome. In its tests, the trailer’s rear structure bypassed the car’s crumple zones and intruded deep into the passenger compartment, resulting in potentially fatal injuries despite the vehicle carrying a 5-star safety rating.

The comparison highlights an important point. A car’s safety in an underrun crash depends not only on its own crash structure, airbags and ADAS, but also on the design and effectiveness of the truck’s rear underrun protection. If the barrier fails to prevent the car from sliding underneath, even the safest passenger vehicle may not be able to fully protect its occupants. Euro NCAP describes the underrun barrier as the final line of defence when both the driver and ADAS fail to avoid a collision.

Euro NCAP recommends USA’s IIHS TOUGHGUARD

The crash tests have highlighted significant shortcomings in the current R58.03 European underrun protection regulation. Euro NCAP believes occupant protection can be substantially improved by adopting the voluntary IIHS TOUGHGUARD standard already used across much of the United States.

In Euro NCAP’s own testing, trailers fitted with the IIHS TOUGHGUARD barrier prevented the car from sliding underneath. This allowed the vehicle’s crumple zones to absorb impact energy as intended, greatly improving occupant protection. Introduced in 2017, IIHS TOUGHGUARD is estimated to be fitted on around 70% of new trailers sold in the United States.

The stronger design uses reinforced steel beams, improved mounting brackets and enhanced energy-absorbing structures that remain effective even during offset impacts. Euro NCAP has urged regulators in Europe and the UK to update existing R58.03 standards to match the IIHS benchmark. It has also called on trailer manufacturers to voluntarily fit stronger underrun guards on new trailers and develop retrofit solutions for existing fleets instead of waiting for regulations to change.