ZF made headlines in 2019 with a pre-crash external side-airbag concept designed to create an extra lateral crumple zone before a side impact. The dramatic part was the giant bag outside the car. The harder engineering problem was deciding—within fractions of a second—that a crash was truly unavoidable and that deployment would help rather than create a new hazard.
The vehicle has to detect the threat before contact
Traditional airbags respond to crash sensors after impact begins. A pre-crash external system needs environment sensors to identify another vehicle or obstacle approaching the side while there is still time to act.
“Something is close” is not enough
ZF described algorithms using the vehicle’s sensor data to determine whether a collision is imminent and whether deployment is appropriate. False positives matter because an external airbag is not a warning light that can simply switch off again.
The bag has to become useful before the other vehicle arrives
ZF’s prototype used a large external side airbag intended to deploy immediately before impact. The company said tests suggested that the additional lateral crumple zone could reduce occupant injury severity in side impacts by up to 40% under tested conditions.
Active and passive safety have to cooperate
Active sensing
Radar, cameras or other sensors estimate the outside threat.
Decision software
The vehicle calculates whether impact is sufficiently likely and whether the timing window exists.
Passive protection
The airbag creates additional structure only after the decision has been made.
Occupant systems
Seatbelts, interior airbags and vehicle structure still remain part of the protection strategy.
A prototype can change safety engineering even before mass adoption
The external-airbag idea illustrated a broader shift: vehicles increasingly use pre-crash information to prepare restraint systems before the collision is fully underway. The important innovation was not only the bag. It was the integration of sensing, prediction and occupant protection.
The airbag was the visible part of an invisible timing problem
Pre-crash safety works only when the car can see, predict and act with extremely high confidence. That is why a spectacular prototype is the beginning of the engineering story, not the end.