Although seat belts do not degrade as quickly as parts of a vehicle that need frequent servicing, there are some instances when seat belts should be replaced. Seat belts, like car seats and air bags, are considered by the National Highway Traffic Safety Administration to be single-use items.

Seat belts are designed to work just once — protecting and immobilizing a passenger in the event of a crash. Seat belts are more advanced than they were when first introduced in vehicles. Early seat belts were options on cars. It wasn’t until Saab first introduced seat belts fitted as standard in 1958 that the practice became commonplace.

Since then, seat belts have been redesigned many times to make them even more effective. They have a pretensioner, which reels back slack on the seat belt. Pretensioners preemptively tighten the belt to prevent the occupant from jerking forward in a crash. They can be activated in a bad crash or any crash severe enough to deploy an air bag.

Seat belts also are equipped with locking retractors, which afford the seated occupant some movement while still providing a means to limit movement in the event of a crash. Retractors equipped with inertial locking mechanisms stop the belt from extending off the reel during severe deceleration.

Both of these safety belt components may effectively work only once. After an accident, the ability of pretensioners and retractors may be compromised. The fabric seat belt itself also may have been marginally stretched out in the crash. It’s adviseable to replace any seat belts that were in use during a crash to ensure the belts will offer the same measure of protection should a collision occur in the future.

Some manufacturers also recommend changing all of the safety belts in the vehicle, even if they weren’t in use at the time of the crash. The vehicle owner’s manual should include recommendations regarding when to change seat belts. If it does not, drivers can speak with a dealership mechanic.

Seat belts that are frayed or do not operate properly, regardless of whether or not they were involved in a crash, also should be replaced. Some safety experts advise having seat belts inspected and possibly replaced after 10 to 15 years of use. One can never tell how older seat belts will stand up in the event of an accident.

If the seat belts have a built-in indicator, verify that they have not been stretched during regular wear to warrant replacement. Seat belts can protect passengers only if they are in good working form. They likely need replacement after a collision.