Final answer:
The most crucial factor in lessening injury during a car crash is increasing the impact time through car design, such as with crumple zones and airbags which reduce injury severity by spreading out the force over a longer period.
Step-by-step explanation:
The most important factor that affects the amount of injury a patient suffers as a result of a car crash is how the car design increases the time of impact to reduce the force exerted on the passengers. According to physics, the impulse experienced by an object or in this case, a person is the product of the force applied and the duration over which it is applied. If the duration is increased, the force exerted is reduced for the same change in momentum, which is why crumple zones in modern cars that deform during a collision are critical in protecting the occupants.
This design element decreases the force on the occupants by spreading it out over a longer period, leading to less severe injuries. The presence of airbags and other safety features also contribute to this by ensuring that the occupants come to a stop more slowly, as opposed to a sudden, forceful stop which could result in more serious injuries.