An Evaluation of the
Effects of Glass-Plastic Windshield Glazing in Passenger Cars
Glenn G. Parsons
Abstract
Following revision of the applicable Federal safety
standard in 1983, two motor vehicle manufacturers equipped some of their cars with
glass-plastic windshields for testing in rental fleets. One company also installed the
windshield in regular production cars for a brief period. The windshield was thought to
have high potential for reducing windshield-caused lacerations to occupants involved in
crashes. There were also concerns over the durability of the product. This study is an
evaluation of the safety, durability, and cost of glass-plastic windshield glazing. It is
based on analyses of data from State crash files, fleet tests, and other sources. The
study findings are:
- Safety. Crash data indicate that the injury
reduction potential of glass-plastic windshields is substantially less than predicted.
- Durability. Fleet and warranty claim data indicate
that durability problems are greater than anticipated.
- Costs. A glass-plastic windshield adds $65 to the
cost of a new car. Additional "durability" costs would also accrue. Replacement
cost is estimated to exceed $1,700.
- Today's high rates of safety belt use, coupled with the
growing number of air bag-equipped cars, mean that windshield-caused injuries have
decreased and will continue to decline.
Executive Summary
Introduction
Under Executive Order 12866 (and prior Executive Order
12291), the National Highway Traffic Safety Administration (NHTSA) has been directed to
carry out periodic reviews of the automotive safety regulations which it has issued. These
reviews provide a means of measuring the impacts of those regulations, in terms of the
benefits which accrue to, and the costs which are imposed upon, the American public.
This study is a review of the effects of glass-plastic
windshield glazing. It is NHTSA's second review of the effects of windshield glazing in
passenger cars. The first study, published in 1985, evaluated the safety benefits and
costs of conventional windshield glazing which has been standard equipment in
American-made vehicles since 1966. The conventional windshield, often referred to as the
"HPR" (or High Penetration Resistant) windshield, was found to be a major safety
improvement over previous glazing designs, and was credited with bringing about a major
reduction in the frequency and severity of head and facial injuries which resulted from
occupants being thrown against the windshield in crashes. The primary benefit of the HPR
design was a large reduction in the more severe facial lacerations and fractures, with a
more modest reduction in less severe, or minor lacerations. These benefits were attributed
to improved production techniques which significantly increased the penetration resistance
of the windshield. Occupant penetration of the windshield is generally associated with
more severe injury.
Federal Motor Vehicle Safety Standard (FMVSS) No. 205,
issued by NHTSA in January 1968, prescribes safety requirements for all glazing materials
used in motor vehicles, including the windshield, the windows, and any interior
partitions. The purpose of this standard is to: (1) reduce injuries resulting from impact
with the glazing surfaces; (2) minimize the possibility of occupants being thrown through
the windshield in collisions; and (3) ensure a necessary degree of transparency in the
glazing for driver visibility. In 1983, the agency amended FMVSS No. 205 to permit the use
of a new type of glazing, known as "glass-plastic" glazing. This change to the
standard did not require the use of glass-plastic glazing, but rather permitted the use of
this material at the option of the motor vehicle manufacturer.
The essential promising aspect of the glass-plastic
windshield was its considered potential to further reduce windshield-induced lacerations.
While the HPR windshield had substantially reduced these types of injuries, a considerable
number still remained, primarily those in the minor severity category. The conventional
windshield is a three-ply design consisting of two plies of glass sandwiched around a thin
interply of plastic (polyvinylbutyral). The glass- plastic windshield is of similar design
with the exception of an inner plastic liner (polyurethane) that is bonded to the inside
glass ply -- i.e., the side of the windshield which faces the passenger compartment. The
inner plastic liner would be expected to provide additional protection (over that afforded
by the HPR design) against cuts from broken glass shards produced when occupants collide
with the windshield during crashes. The plastic liner would provide a "containment
mechanism" for the broken pieces of glass, thereby reducing the occupant's chances of
coming into direct contact with the sharp edges of these glass fragments. While
glass-plastic windshields were expected to substantially reduce lacerative injuries, there
was concern that the inner plastic layer, being a much softer material than glass, could
be susceptible to damage that could degrade driver visibility and reduce windshield
durability. There was also some concern that the stiffer surface presented by the 4-ply
glass-plastic windshield might contribute to a greater incidence of blunt impact injuries
(i.e., concussions, contusions, complaint of pain). Overall, however, the potential safety
gain from glass-plastic glazing was believed to far outweigh possible durability and other
problems, and, therefore, the agency elected to permit (but not require) its use in order
that real-world data might be developed to provide an evaluation of these issues.
Glass-plastic glazing was first developed in France by the
Saint Gobain Vitrage Company, and some of the European car companies (among them, Peugeot,
Porsche, and Mercedes) had fitted a limited number of their vehicles with glass-plastic
windshields in the late 1970's and early 1980's to test the material in the market place.
In the early 1980's, two domestic companies, General Motors and Ford, equipped a number of
their vehicles with glass-plastic windshields and placed them in rental fleets to field
test the windshields. Later, in 1984, General Motors introduced the glass-plastic
windshield to the general public, by making it standard equipment on one of its luxury car
models, the Cadillac Seville Elegante. Early in the 1985 model year, the windshield was
made standard on all Seville models, and for model years 1986 and 1987, the company
expanded its use of the plastic windshield glazing, making it standard on all Cadillac
Eldorados, all Buick Rivieras, all Oldsmobile Toronados, and all Pontiac 6000 STE'S. At
the end of the 1987 model year, however, General Motors discontinued all use of
glass-plastic windshields in its regular production vehicles. GM stated that the reason
for discontinuing installation of the windshield ws because of its high replacement costs
for customers and high warranty costs for the company. It is estimated that approximately
210,000 regular production GM cars with glass-plastic windshields were produced before the
company halted use of the windshield. No other car companies, domestic or import, have
since equipped any of their U. S. marketed regular production vehicles with glass-plastic
glazing.
Study Objectives and Data Sources
The objectives of this study are threefold:
(1) to estimate the extent to which glass-plastic
windshield glazing could reduce lacerative injuries resulting from occupant contact with
the windshield in crashes,
(2) to assess the nature, extent, and consequence of
durability problems that could be experienced if glass-plastic windshields were installed
in vehicles on a volume basis, and
(3) to estimate the costs that would be incurred from the
use of glass-plastic windshields in motor vehicles.
The injury reduction effect of glass-plastic windshields
is primarily based on the analysis of police reported crash data from three States, New
York, Pennsylvania, and Indiana. State data -- in particular data from New York State --
constituted a major source of the information utilized in NHTSA's earlier study of the
effects of HPR windshield glazing. Although not without certain limitations, these States
provide detailed injury data in their automated crash files, such as type of injury and
body location of injury, which are necessary to estimate the effect of the windshield
glazing. The analyses are based on comparing the rate of bleeding injuries (primarily to
the head and face) sustained by front seat occupants of glass-plastic vehicles (1985,
1986, and 1987 GM vehicles) with the rates of similar types of injuries sustained by front
seat occupants of a control sample of vehicles. Bleeding injuries are considered to be
generally synonymous with lacerative injuries. The control vehicles are GM cars of similar
size, weight, and price range, which are equipped with conventional (i.e., HPR)
windshields. The crash and injury results of special fleet tests of vehicles equipped with
glass-plastic windshields are also reviewed.
The durability information is based primarily on the GM
and Ford rental fleet field tests, together with other information, including warranty
data, obtained from these manufacturers. The costs of glass-plastic glazing are based on
earlier estimates made by the agency, on information solicited from the motor vehicle
manufacturers, and on data on the aftermarket replacement costs of the glazing. A consumer
survey of vehicle owners had originally been planned to obtain "first-hand"
information on owner experience with the windshields, but budgetary priorities precluded
the agency from conducting the survey.
It should be noted that major advances in motor vehicle
safety have occurred since the agency amended FMVSS 205 in 1983 to permit the use of
glass-plastic glazing. Safety belt use has increased to levels of over 60 percent compared
to a low 14 percent in 1983. Also, air bags not only have received wide acceptance, but
will be required in all new cars and light trucks by the late 1990's. These significant
increases in occupant protection mean that the numbers of occupants who impact the
windshield (thereby being exposed to lacerative injuries from broken glass) have been
substantially reduced and will continue to diminish. Hence, the magnitude of the safety
problem originally targeted by glass-plastic windshield glazing is being substantially
reduced. This situation contrasts rather sharply with the occupant restraint picture in
1983 when NHTSA amended Standard 205. At that time, the agency recognized that substantial
changes in the availability and use of passive restraints could alter the need for the
additional occupant protection qualities expected from glass- plastic glazing. However, if
automatic restraints were eventually installed in passenger cars, the agency believed that
they would primarily be passive belt designs (as opposed to air bag systems) and that a
substantial portion of motorists would elect not to use them. This was also prior to the
period of State Mandatory Restraint Use Laws and other developments which have since
fostered marked increases in the use of safety belt systems, both active and passive.
Following are the principal findings and conclusions of
this study:
Findings
Injury Reduction
- The analysis of available crash data from three States
found no reduction in bleeding (or lacerative) injuries for vehicles equipped with
glass-plastic windshields as compared to vehicles equipped with conventional windshields.
Small sample sizes of injury data plus other restrictions in the data serve to limit the
reliability of this finding, and the results are not interpreted as precluding that
glass-plastic windshields may have a beneficial effect in reducing lacerative injuries.
- Data from fleet operations were insufficient for analyses
with respect to the injury reduction potential of glass-plastic glazing. However, these
data did provide limited evidence that lacerations do indeed result from glass-plastic
glazing. lacerations from glass-plastic glazing were described as
"skin-splitting", or "tearing-type" injuries, resulting from blunt
impact with the plastic inner liner of the windshield, rather than lacerations from broken
glass. In these injury cases, the windshield glass was broken, but the broken pieces did
not penetrate through the plastic inner liner.
Durability
- Although not necessarily representative of the motoring
public in general, data from rental fleet operations indicates that durability issues
associated with glass-plastic windshields could be of significant concern. Primarily,
these issues revolve around the susceptibility of the plastic inner liner to damage (i.e.,
cuts, scratches) from the everyday operating environment:
- in one fleet, an estimated 42 percent of the windshields were
found to have moderate-to-heavy scratches and cuts after 15 months of operation. The
vehicle manufacturer was concerned that this damage might not be acceptable to longer term
owners.
- in another fleet, 44 to 48 percent of the windshields
were replaced due to damage occurring during fleet operations, and in order to
"prepare the vehicles for resale" at the end of the one to one and one-half year
test period. Available data indicate a replacement rate of 10 to 15 percent for
conventional windshields in comparable rental fleet service.
- all glass-plastic windshields replaced in the rental
fleets were replaced with conventional windshields.
- Warranty claim data from the one manufacturer which briefly
introduced glass-plastic windshield glazing to the general public also indicated that
durability of the material was a concern. Warranty claim rates of 12.6 percent, based on
12 months/ 12, 000 miles of service, were more than four times as high as for conventional
windshields. Vehicle owners cited poor visibility and scratching/scoring as the primary
reasons for windshield replacement.
Costs
- It is estimated that a glass-plastic windshield, if
installed in volume quantities, would add $65 to the cost of a new car. Additional
consumer costs would be expected due to damaged windshields that would have to be replaced
after the new vehicle warranty period expired, or for damage not covered under the
warranty.
- Data on aftermarket windshield replacement show the cost of
replacing a glass-plastic windshield to be over $1,700, or more than $1,200 above the cost
of replacing a conventional windshield. To what extent this high cost is due to limited
production quantities or to glass replacement shop inexperience/unfamiliarity with the
glass-plastic glazing, as opposed to lower durability characteristics of the glass-plastic
windshield, cannot be answered with available data. Due to this very high cost, it is
believed that almost all aftermarket replacements of glass-plastic windshields have been
made with conventional windshields rather than the original equipment glass-plastic
windshields.
- Both motor vehicle and glass manufacturers cited high costs
as the reason why the market for glass-plastic windshields failed to develop.
Conclusions
- Analyses of available crash information, because of small
sample sizes and other limitations in the data, are insufficient to support firm
conclusions. Nevertheless, the analyses of State crash data, together with limited
evidence from fleet crash data, do suggest that the actual lacerative injury reduction
benefits from glass-plastic lazing are likely to be substantially less than the essential
elimination of windshield-caused lacerations, as originally projected by the agency. While
there is evidence that the inner plastic liner does serve to reduce the occupant's chances
of coming into contact with broken glass shards, lacerations can still occur from blunt
impact with the inner liner. Data are insufficient to determine whether these injuries
differ from the lacerations due to conventional windshields, with respect to severity or
facial scarring potential.
- Data from rental fleet operations and manufacturer warranty
claims indicate that durability problems are greater than originally anticipated by the
agency. Potential solutions to these durability concerns, including windshield warning
labels and "special care" information in the vehicle owners manual, did not
appear sufficient to prevent damage from occurring to the plastic inner liner, nor
warranty claim rates several times higher than for conventional windshields. The high
replacement cost of glass-plastic windshields is also believed to reflect, at least
partially, the lower durability characteristics of the glazing.
- Depending on the nature and extent, damage to the plastic
inner liner of the glass-plastic windshield could degrade driver visibility. thereby
creating a safety concern. Insufficient data are available to quantify the significance of
this issue. Also, the indicated widespread replacement of damaged glass-plastic
windshields with conventional windshields, due to cost or other considerations, has the
effect of negating any safety benefits inherent in the glass-plastic glazing.
- The higher component and durability costs of the
glass-plastic windshield, compared to that for a conventional windshield, would appear to
be high relative to the injury reduction benefits that might be realized from the glazing.
- Today's high rates of safety belt use, together with the
universal acceptance of air bags - in contrast to the situation in 1983 when the agency
permitted the use of glass-plastic glazing - mean that the size of the lacerative injury
problem due to occupant-windshield contact is substantially smaller than it was a decade
ago and will continue to diminish.
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