Windows that Cut

Designed properly, the glass in motor vehicles should protect drivers and passengers, not lacerate and cause them serious injury.  Windows and windshields, necessary for the safe operation of the vehicle, can and should also help prevent ejection in automobile collisions. Manufacturers also rely on glazing as a structural member of the vehicle; that is, the glazing serves as a support for the roof and sides of the automobile. Unfortunately, typical glazing in cars today does not actually afford these basic protections, despite the availability of tested and demonstrated solutions.

The Damage Done: Scope of the Problem

In 1998, according to the National Center for Statistics and Analysis (NCSA), 60,884 passenger vehicle occupants involved in traffic collisions were ejected, either completely or partially, through windshields, side windows, rear windows and roof windows.  More than half were hurled through the right and left front-seat side windows.

That same year, 280,424 passenger vehicle occupants involved in traffic collisions were lacerated by motor vehicle glass.  Well over half – 161,756 – were cut by flying glass rather than by contact with a windshield or window.  Of the remaining 118,668, almost 100,000 were cut by contact with the windshield, and some 17,000 were cut by contact with the driver's side window, according to an analysis of data compiled by the National Highway Traffic Safety Administration.

Automobile manufacturers continue to gloss over these risks posed by glazing in their vehicles, despite clear evidence that current motor vehicle glass causes injuries and blindness, does not adequately protect against ejection from the vehicle, and offers virtually no structural protection in a collision.  Alternatives are ignored that could reduce these injuries substantially.

The common perception is that most ejected vehicle occupants are hurled through the windshield.  The facts speak otherwise.  In the early 1980s, internal studies by automobile manufacturers showed that almost 60 percent of driver and passenger ejections occurred through windows other than the windshield.  These same studies recommended that impenetrable side glazing be incorporated as a countermeasure to prevent ejection.  Manufacturers declined to do what their own engineers recommend, however, once again presumably placing profits ahead of safety.

Types of Glass

Federal regulations currently allow three types of glass for use in motor vehicles:  laminated, tempered, and glass-plastic.

Laminated Glass

Laminated glass is allowed in all vehicle windows but is used typically only in windshields.  It consists of two pieces of annealed glass (created through a process of heating and cooling to make the glass less brittle), sandwiched with a layer of adhesive material.  Over the years, the adhesive has consisted of cellulose, plastic, polyurethane and, currently, polyvinyl butyral.

Laminated glass is about three times stronger than ordinary annealed glass.  Although the glass still breaks the way ordinary plate glass does, the fragments adhere to the internal material, which keeps it from flying about the passenger compartment.  The fractured glass is limited to a small area radiating outward in a star pattern from the initial break. The laminate therefore acts as a "safety net," absorbing energy from the contact while keeping the occupant inside the vehicle.  This reduces the possibility of brain injury and ejection, and enhances the possibility of the glazing adding to the vehicle's structure.

Several upscale automobile manfacturers – BMW, Mercedes, Peugot, Audi and Volvo – take advantage of the protection afforded by laminated glass by offering it in side windows in at least some of their models.  Also, DaimlerChrysler Mexico manufactures two models, Cirrus and Stratus, with laminated side windows as an anti-theft feature.  Otherwise, the use of laminated glass is largely limited to windshields.

Tempered Glass

Plate glass that has been heat-tempered to increase its strength is three to five times stronger than annealed glass, but when it does break, it shatters, offering no protection against ejection from the vehicle.  Further, when tempered glass shatters and leaves the window opening, the vehicle loses an element of its' roof's and sides' structural support.

The tempering process also affects the way the glass breaks.  Advocates claim that fractured pieces of tempered glass are small and have edges that are less sharp than pieces of annealed glass, but this is not accurate.

Tempered glass breaks from the inside out, which causes the "clustering" effect of the glass.  These clusters can be several inches in diameter and have jagged edges that do lacerate.

Glass-Plastic Glazing

Glass-plastic consists of either laminated or tempered glass with a clear "plastic" laminate on the side of the glass that faces the occupants.  The benefits are obvious:  the inner-layer plastic not only protects against flying glass, it also helps hold the glass together, thus helping prevent ejection and retain the structural support features afforded by the glazing. 

The Regulators and the Regulated

The automotive industry resists using glass-plastic, however, citing durability and processing concerns. Advocates insist that the real reason for the industry's reluctance is concern for profits.  In 1983, Federal Motor Vehicle Safety Standard 205, which governs motor vehicle glazing, was amended to permit use of laminated glass-plastic glazing in windshields and other windows of motor vehicles.  The Standard now permits (but does not require) the use of annealed laminated glass-plastic and tempered glass-plastic.  In other words, government regulation allows manufacturers to use the safer glass and, for the most part, they refuse.

Despite decades of knowledge about the risks posed by its windshields and windows, the auto industry continues to resist widespread use of safer glass in vehicles.  The National Highway Traffic Safety Administration (NHTSA) sets minimum standards, which auto-makers are free to exceed, but when it comes to installing safer windows in their vehicles, most have declined to do so.  A look at the "Purpose" section  of Federal Motor Vehicle Safety Standard 205 makes it clear that tempered glass does not meet the explicitly-stated purpose of the Standard.  FMVSS 205 sets forth its intended purpose:

Meanwhile, the only pressure on manufacturers to use safer glass comes from safety lawyers who sue automakers when their vehicle glazing harms, rather than protects, people in crashes. 

(03/12/01)