Passive Safety System

A passive safety system refers to the suite of safety technologies designed to minimise injuries to vehicle occupants and pedestrians through structural design and restraint systems when a collision becomes unavoidable.

If active safety is all about "accident prevention", then passive safety serves as the "last line of defence" to protect lives during a crash.

Core Components

A passive safety system mainly comprises the following key components, all working in unison at the moment of impact:

Rigid Body Structure
This forms the cornerstone of passive safety. Modern cars widely adopt a "safety cage" construction with front and rear crumple zones that deform progressively like an accordion during a collision to absorb the brunt of the impact energy. Meanwhile, the central cabin utilises ultra-high-strength steel to form a rigid safety cell, ensuring the survival space for occupants remains intact. For instance, the A-pillars of a race car's monocoque chassis must withstand up to 7.5 tonnes of load without structural failure.

Restraint Systems

• Seatbelts: The most fundamental and effective protective restraint. Pre-tensioner seatbelts instantly retract upon impact to eliminate slack, firmly securing occupants to their seats. Airbags essentially serve as supplementary restraint systems (SRS) and must work in tandem with seatbelts to deliver optimal protection.

• Airbags: Deploying within 0.03 seconds during a crash, airbags create a protective cushion between occupants and hard surfaces such as the steering wheel and dashboard. Modern vehicles are typically equipped with dual front airbags, side airbags, curtain airbags, and even knee airbags to deliver comprehensive surround protection.

• Active Headrests: These automatically shift forward during a rear-end collision to support the head, significantly reducing the risk of whiplash injuries caused by the sudden rebound motion of the cervical spine.

Occupant and Pedestrian Protection
The cabin incorporates soft-touch materials, a collapsible steering column, and a collapsible brake pedal mechanism to prevent intrusive components from injuring occupants in a severe crash. On the outside, optimised bumper and bonnet structures—along with features like an active pop-up bonnet—help provide a cushioning effect to mitigate pedestrian injuries during an impact.

Technology Trends

Passive safety is evolving from conventional physical shielding towards intelligent integration. In the electric vehicle (EV) era, the high-voltage system can be automatically cut off via sensor linkage upon impact to prevent secondary electrocution risks. Moving forward, passive safety will integrate deeply with active safety systems, where on-board sensors predict an imminent collision, prime the seat positions, and pre-tension seatbelts ahead of impact to brace occupants beforehand.