What type of safety restraint should always be locked for maximum effectiveness?

The combined lap and shoulder belt is designed to provide the best possible protection for passengers, especially children. When properly locked, this type of restraint system secures the child more effectively by minimizing movement during a crash. The lap portion of the belt holds the child down in the seat to prevent sliding under the belt, which can lead to serious injury during a collision. The shoulder belt helps to keep the upper body restrained, reducing the risk of head and upper body injuries.

For maximum effectiveness, the locking mechanism on the combined lap and shoulder belt can also help to prevent the belt from loosening while in use, ensuring that it stays snugly fitted against the child's body. This is essential for maintaining the proper positioning of the seat belt, which is critical for safety in the event of an accident.

Other types of restraints may not have the same safety features or locking mechanism that ensures a secure fit. For instance, a lap belt alone does not distribute crash forces across the strongest parts of the body. A shoulder belt alone can be ineffective if not used in conjunction with a lap belt. A booster seat is designed to raise a child up so that a seat belt fits properly, but it also relies on the proper use of lap and shoulder belts for safety.