|
|
November 2005
Safety glass used in vehicle windshields has been designed as a laminated system to resist penetration. A windshield can withstand a severe blow and show extensive cracking, yet protect the occupants by resisting penetration by all or parts of the test article. Crash records are not sufficiently detailed to tell us how the damage to a windshield relates to the severity of a crash. However there is a need to be able to evaluate various safety features by observing the results of crash tests.
Report 350 states:
Detached elements, fragments or other debris from the test article should not penetrate or show potential for penetrating the occupant compartment, or present an undue hazard to other traffic, pedestrians, or personnel in a work zone. Deformations of, or intrusions into, the occupant compartment that could cause serious injuries should not be permitted.
This provision has been interpreted in different ways by the crash test agencies when evaluating windshield damage resulting from tests with category 2 work zone devices. The most conservative evaluations have failed a device when the cracking extended to the inner layer of glass. The most liberal interpretation considered the test article acceptable even when the entire windshield was shattered sending glass particles into the occupant compartment, as long as the test article itself did not penetrate the windshield. The ability of the driver to see through the damaged windshield also must be considered. An informal survey conducted during the Transportation Research Board's meetings of January 1999, showed a similar diversity of opinion among researchers, manufacturers, and users of the devices.
In FHWA's July 25, 1997, memorandum, it was suggested that windshield damage and intrusion each be rated on a scale. Those scales did not classify the damage as passing or failing. Based upon full-scale crash testing FHWA has reviewed subsequent to that memorandum, the following seven classes of damage are offered as a guideline for evaluating windshield damage. It is realized that there is still room for interpretation between these classes, but that some measure of consistency will be introduced. Sketches are included as an aid in describing the damage and assessing the results. Please note that the amount and extent of cracking shown in the sketches is far less than will be seen in a real windshield.
Case 1. Fail: Any impact that causes a hole through the windshield glass whether or not part of the test article enters the occupant compartment.
Case 2. Fail: Any impact that destroys or deforms the windshield to the extent that it separates from the frame.
Case 3. Fail: Any impact where the windshield is cracked overall to such a degree that the driver cannot readily see to navigate.
Case 4. Pass: Any impact where the windshield is cracked overall and the windshield deflects in towards the occupants without causing a hole in the plastic layer. Glass particles from the inner layer of glass are permitted in the passenger compartment. The driver can still readily see through the damage and bring the vehicle to a safe stop. It is desirable that the maximum permanent deflection of the windshield not exceed 55 mm (2 inches). A maximum permanent deflection exceeding 75 mm (3 inches) shall be considered a failure.
Case 5. Pass: An impact that causes a roughly circular area of localized cracking / shattering completely obscuring vision to a diameter of no greater than one foot. No penetration of the test article through the glass occurs. Extensive cracking throughout the remainder of the windshield is permitted but no deformation occurs other than at the point(s) of impact.
Case 6. Pass: An impact on the roof line that causes shattering of the windshield near the point of impact and/or other cracking that extends throughout the windshield. (This is primarily for taller devices that "bridge" between the front of the hood and the roof.)
Case 7. Pass: An impact that causes only minor cracking or dings on the windshield. (Not illustrated.)
The NCHRP committee pursuing the next generation crash test guidance should consider guidelines for evaluating passenger compartment intrusion. These seven criteria may be used as a starting point for windshield damage. FHWA solicits comments from all concerned as to the appropriateness of these criteria, both in terms of measuring windshield damage using these seven classes, and in terms of expected injury severity in real-world crashes. Please contact Mr. Nicholas Artimovich of the Office of Safety Design with comments or questions regarding these guidelines at (202) 366-1331 or via E-mail at nick.artimovich@fhwa.dot.gov.
 |
Case 1: Impact causes a hole in the windshield |
 |
Case 2: Impact causes separation of windshield from frame. |
 |
Case 3: Significant overall damage. Driver cannot readily see ahead to navigate
to a safe stop. |
 |
Case 4: Significant overall damage but no hole. Driver can readily see to bring
the vehicle to a safe stop. |
 |
Case 5: Significant local damage but no hole. |
 |
Case 6: Significant damage where test object struck roof line but caused no
penetration of windshield nor separation of windshield from roof. |
[The black areas above indicate extensive damage to the glass restricting visibility, and some deflection of the windshield inward. The white dot in Case 1 indicates a hole. The white area at the top of case 2 indicates separation of the windshield from the frame.]
