Seat Belts are a safety device inimical to the modern car, and therefore a significant design feature. Seatbelts, before 1955, were almost optional in cars, and indeed many were manufactured without them. That deaths occurred in collisions explicitly from the body of the driver and passengers expressing their momentum as velocity inherited from the car, and then as kinetic energy, makes the invention of seatbelts and their slow adoption rate all the more puzzling.
However, in the first four decades of the 20th century, cars and their performance were not of a life threatening nature, typically. Certainl, racing cars had seat belts and harnesses, but until 1935, of a perfunctory nature - the belt was to keep the pilot in the car, rather than save his life.
The crucial period of 1929-1935 set the need for a seatbelt in motion. Before that time, the Ford Model T did not have life threatening performance, and was the most numinous car in the world. After 1929, vehicles around the world were capable of exceeding 35 mph / 50 kph, and thus head on collisions were now possibly fatal to occupants. And yet, seatbelts were not perceived as a necessity, and even 'for sissys' at this period.
After WWII, technology for aeroplane engines was translated into production engines for road cars, and performance increased and increased, thus creating the situation in 1955 where deaths as a result of collision were becoming excessive in the USA and Europe, and not inconsiderable in the rest of the world.
Changes in legal requirements for cars saw the widespread adoption of lap seat belts in the USA, and the three-point belt in Europe. Fatalities fell, though injury still was a problem - which led to the creation of the airbag, and this turn is another story.
Today, seatbelts are able to protect us from death (though not completely from injury), and therefore have become sina qua non. Today's driver and passenger does not leave home without first buckling up, and its rare to see a car being driven without this obvious safety feature. Reminders in the form of audio electronics help drivers to be aware of this, and there are often lights on the dashboard as well as voices from the navigation system in luxury cars.
A matter of size - the creation of seatbelt extender
A sad comment on modern life is that as we grow older, we invariably grow bigger. In modern cars, human size is not a problem in terms of design constraint, and so the seatbelt systems are usually able to cope with even the biggest passengers.
But what about older cars, from say the late 1970's and early 1980's ? More often than not, these vehicles have safety belt systems, but these in turn are often not acceptable from a comfort point of view.
In addition, safety belt systems are often spanned in for safety when transporting bulky or massy items inside vehicles such as vans, SUV's and station wagons/estate cars, which also very often do not have adequate protection or tiedown systems as part of their design to permit safety in transit.
For these vehicle system shortfalls, the seatbelt extender has been developed.
Seatbelt extenders consist of a length of belt webbing, terminating on one side with a press-button seat belt clip, and on the other with buckle for insertion in the equivalent clip. Extenders are available for most brands for motor vehicle, and are also available for FAA seatbelt systems such as those found in airliners.
The belt webbing is of equivalent material strength to that fitted to the car in question (and sometimes better), as are the buckles and clips.
Pros and cons
Pros of the seatbelt extender are:
- Better accommodation in vehicles with limited seat belt travel
- Ability to tie down bulky/massy items within vehicle interiors, and when folding down seats
- Seatbelt system is not modified for application
- Extender is visually equivalent to rest of vehicle interior
- Extenders are not tested in crash testing with the vehicles passenger restraint system
- Failure is now more likely in comparison with OEM restrains, and in conjunction with them
- Getting in and out of the vehicle using the extender varies from being ungainly to undignified
- Confusion can result during use by passengers and driver unfamiliar with the technology
By far and away the most frightening thing about seat belt extenders is the likelyhood of them being a safety hazard for the vehicle and occupant during a collision. While the extender offers near equivalent safety of a belt with a sufficient length, it is possible that the supports of the seat itself and of the belt are inadequate for absorbing the kinetic energy of masses not calculated for by designers. The extender may thus compromise safety by extending the load margins beyond the safe limit.
Manufacturing processes of an extender are also a significant factor - where possible, if a manufacturer of the belt is OEM to the vehicle, e.g. a Bosch extender for a VW equipped with a Bosch seatbelt system, then the reliability of the extender will be far better than that of a no-name brand manufactured by an unknown manufacturer.
Seat belt extenders serve useful functions in permitting safety for occupants and cargoes within vehicles that would otherwise not provide sufficient slack in their belt systems to accommodate these two types of loading.
Consideration should be made by the user of the system, with caveats in the forefront of the mind with regard to safety.
Apart from those considerations, extenders are a useful product that help to provide safety in situations where OEM equipment may be somewhat inadequate in special circumstances.