Occupant protection — within a vehicle's supplementary restraint system (SRS), which component is the most widely used and provides primary restraint in crashes?

Introduction / Context:
Supplementary restraint system (SRS) is an umbrella term for passive safety devices designed to work together to mitigate occupant injury in a crash. While airbags get visual attention, the primary and most widely used restraint remains the seat belt, which restrains occupant motion and manages crash energy via controlled load limiting and pre-tensioning.

Given Data / Assumptions:

• SRS includes seat belts, airbags, sensors, pretensioners, and control modules.
• Seat belts are worn on every trip (compliance assumed), across all seating positions.
• Airbags supplement but do not replace belt restraint.

Concept / Approach:

Seat belts provide primary restraint by preventing occupant ejection, controlling deceleration loads on the chest/pelvis, and properly positioning occupants for effective airbag deployment. Airbags deploy only in certain crash severities/directions and are explicitly designed to supplement belts. Brakes and steering are active control systems for avoiding crashes, not SRS components.

Step-by-Step Solution:

Verification / Alternative check:

Regulatory and epidemiological data consistently show belts as the single most effective in-vehicle safety device for injury reduction in most crash modes, with airbags providing additional benefit when used in combination.

Why Other Options Are Wrong:

Brake — not an SRS component; it is an active system for speed control.
Airbag — crucial but supplemental; not engaged on every trip and not effective without belts.
Steering — part of vehicle control, not restraint.

Common Pitfalls:

Assuming airbags alone provide sufficient protection; neglecting seat belt usage which is foundational to SRS performance.

Final Answer:

seat belt