January/April 2001

Seeing the Lite
    NHTSA Looks at Enhanced Glazing as a Way to
Reduce the Number of Deaths in Vehicle Rollovers
by Leslie Shaver

The numbers are staggering. 
Each year approximately 7,300 people are killed because of complete or partial ejection through sidelites and moonroofs in vehicles, according to the National Highway Transportation Association (NHTSA).

Of these 7,300 deaths, more than 4,400 are associated with vehicle rollovers. In the early-1990s NHTSA began to evaluate this problem seriously by looking at ways to keep people inside vehicles during rollovers.

“If you keep someone in the car, there is a tremendous survivability benefit,” said Steve Summers, an engineer with NHTSA. “Your odds of fatality greatly increase when you are ejected from the vehicle.”

Luckily, finding solutions to these problems is not difficult. “Though it [the number of window ejections] is significant, it is a relatively-easy-to-address problem,” Summers said.

Since vehicle occupants are ejected through glass, it has come to the forefront as one of the primary areas where improvements can be made (though not the only one—see sidebar below). “Windows can be designed in such a way that keeps people from going out through them,” Summers said.

As NHTSA has evaluated auto glass windows, it has looked at bilaminates, trilaminates and polycarbonates—three types of material that conceivably could replace tempered glass in sidelites, yet hold occupants inside the car during an accident.The use of laminated sidelites, such as those in the Volvo S-series, is steadily increasing as the number of people killed or injured because of complete or partial ejection through sidelites increases.

Voices of Caution
Some auto manufacturers have not jumped aboard the laminated glass (also called Enhanced Protective Glazing) bandwagon. While companies such as Volvo and Audi have put laminated glass in the sidelites of their higher-end models, other manufacturers have not yet incorporated laminated sidelites into their full line of vehicles. 

When NHTSA sent out questions to the public about its alternative glazing program, General Motors of Detroit provided some stirring comments, many of them critical of alternative glazings. 

In the company’s response, it cited several disadvantages to alternative glazing in sidelites including:

- The possibility of glazing puncturing side airbags. Airbags are another product NHTSA is looking at to lessen the amount of side window ejections;

- More severe head and neck injuries for passengers as their heads bang against laminated sidelites, which may not give way as well as tempered glass;

- Possible entrapment in the vehicle because laminated glass and plastics will not break, giving the occupant an escape (as tempered glass does);

- Larger pillars, door frames and rail structures in these vehicles, which could obstruct the view of the driver, making him or her more prone to accidents; 

- Plastic and bilaminate glazings that are susceptible to abrasion and durability problems.

“We believe that alternative glazings have limited potential to prevent occupant ejections,” C. Thomas Terry, director of safety affairs and regulations for GM, said in the company’s response to NHTSA. “The reasons for this are the loss of integrity of the glazings that often occurs in rollover crashes, the necessity for the window to be in the up position at the time of the crash, the extensive design changes required to ‘capture’ the perimeter of the glazing, etc.”

The area of the door holding the perimeter of the glazing is important because it must be fortified to handle the additional pressure an occupant will put on it during a crash. Currently, these frames do not have to absorb weight because the tempered glass in a window breaks during a crash, releasing energy. If the window does hold the occupant inside, the door frames would have to hold this additional force.

When bonded properly, windshields hold this force for years. However, according to Terry, bonding the sidelites to the door would be much more difficult. “You can’t bond the glass when a window goes up and down [like sidelites do],” he said.

The Leading Contender
Of the three contenders, trilaminates seem to offer the most promise. Already in high-end cars in Europe and the United States, these glass-plastic-glass combinations are close relatives of a product found in the automobile for more than 50 years—the windshield.
Surprisingly, the selling point for laminated glass in these cars was not occupant retention during accidents, but theft-resistance. Noise and ultraviolet resistance are also strong selling points.

Would-be car thieves are forced to expend time and energy banging and probing on the sidelites to get in through the windows, instead of just popping tempered glass sidelites. “While tempered glass will shatter, laminated glass will stay adhered to film,” said Terrence Cressy, director of communications for DuPont Laminated Products of Troy, Mich., a polyvinyl butyral maker. “Film will resist the breakthrough.”

Vehicle manufacturers market cars such as this Volvo S-60 promoting the added safety benefits its laminated sidelites offer. Because trilaminates are in cars, the means of producing them are already in place, giving them one advantage over the competition. Currently, trilaminates can be found in the Volvo S60, the Audi 80, the Volvo S80, the Mercedes-Benz S-Class and the Peugeot 607. 

“We have made windshields with trilaminates for years and years,” said Glenn Davis, market manager for glass at PPG Industries in Pittsburgh. “We are aiming to provide a piece of glass that is exactly the same weight as tempered glass. This will be a drop-in replacement.”

Further strengthening the case of trilaminates are NHTSA studies that show the head impact damage for the products it is testing may not cause head injuries. “Generally laminated glass performs well in head-impact tests,” Cressy said. 

There is also a perception that first responders would have a difficult time fighting through laminated sidelites to get to crash victims. While tempered glass is designed to break into pieces upon impact, laminated glass is designed to hold, potentially trapping the occupant in the vehicle.

However, the laminated glass community, with support from highway safety advocates and professionals charged with rescuing people from cars after accidents, say that modern tools, combined with knowledge of how to get through laminated glass, can solve this problem.

“Proper training showing the responders how to identify, cope and adjust techniques for glazing removal will resolve any confusion while confronting the new types of glazing,” said Ronald Shaw, a fire service instructor for Extrication.com, an online service offering information for potential first responders.

There is also a concern among some that laminated sidelites will add increased weight to the vehicle. However, the laminated glass community also takes shots at that argument.

 “There have been inaccurate negative comments about increased weight, when in fact there is a weight reduction when fitting EPG (enhanced protective glazing) in place of tempered glass of comparable thickness,” Robert Esposito, manager of automotive product development for Solutia Inc. of St. Louis, wrote in response to AGRR questions. “At a 5-mm thickness, for example, EPG weighs almost 10 percent less than standard tempered glass, which provides a weight saving of 3.5 kg for all side and rear glazing of an average size vehicle.”

This leads to the last major concern with trilaminates, which is cost. 

With trilaminates you are bending two pieces of glass, in addition to a plastic interlayer. “With tempered glass all you are doing is bending one piece of glass,” Davis said. He estimates that it would cost approximately $100 per car to replace tempered glass with trilaminate sidelites.

Esposito’s figures are a bit heftier. “For a typical side window, the OEM can purchase EPG for an upcharge of about $50 per window,” he said. “So it would cost the car-maker around $200 to equip a vehicle with four EPG window versus today’s tempered glass. Exact costs are a function of specific window designs.”

For his part, Terry estimates it would cost about $20 per window to put in laminated sidelites, plus an initial start-up cost of $500,000.

However, Esposito is confident consumers would see enough value in EPG to pay these prices. “Solutia has conducted extensive market research in the United States and in Europe to identify the value that consumers place on EPG,” he said. “Consumers are willing to pay a $400 to $1200 vehicle upcharge for EPG.”

“Tempered glass is dirt cheap,” said Summers, echoing Davis’ thoughts. “You melt the sand, float it on water and you have glass. Anything we talk about adds cost. The cost may or may not be significant. It depends on who you talk to.”

Glass manufacturers, such as PPG, and PVB makers, such as Solutia and DuPont, do not think the cost is significant. “The cost [of trilaminates] versus the overall cost of the vehicle will be minor,” Cressy said. 

Furthermore, Cressy points out that positives of laminated glass—fewer deaths and serious injuries in rollovers, less air conditioning load due to better ultraviolet resistance and fewer smash-and-grab thefts—will have other financial benefits. “These are tremendous benefits that may be rebated [to consumers] in the form of lower insurance rates,” he said.

However, the auto-makers may have to incur certain costs to properly outfit cars for laminated sidelites, which may explain their reluctance to jump on the laminated sidelite bandwagon. “Depending on existing glass thickness, some vehicles may have to install wider glass tracks and weatherseals to accommodate the glazing thickness,” Esposito said in his response to AGRR.

While these issues may cause concern, the most important modifications auto-makers may have to make is providing enough support around the laminated glass to hold the occupant within. “To provide occupant retention as NHTSA is studying, the door frame and the glazing/door attachment need to be designed to absorb impact energy,” Esposito said. 

Because after all, preventing occupant ejection is NHTSA’s goal.

While trilaminates are becoming more prevalent in sidelites, they are not the only products NHTSA is evaluating. To find out more about the other products NHTSA is evaluating and where NHTSA is in the process of mandating new sidelites, read the next issue of AGRR for the second part of this series. 

The Other Option: Side Airbags

While the glass industry is focusing on how glazing can reduce occupant ejections in rollovers, some in the automotive industry feel that side curtain airbags, with curtains that come out of the rough rails in a car, can reduce or eliminate the need for alternative side glazings. 

“Side airbags have the potential to provide the same benefit as glazing,” said Stephen Summers, an engineer with NHTSA.

“This is a technology that is here,” said C. Thomas Terry, director of safety affairs and regulations for General Motors of Detroit. “Side air bags do two things while laminated glass only does one. A side air bag contains the occupant and reduces the forces of impact on the head and the body, while laminated glass only has the potential to contain the occupant.”

However, DuPont Laminated Products of Troy, Mich., makers of PVB, points out advantages to laminated glass with which side airbags cannot compete. For one, laminated glass offers ultraviolet protection, noise reduction and, of course, theft resistance.

DuPont, in a written response to NHTSA questions, also pointed out another benefit. “Side head air bags are designed to reduce occupant ejection out of windows. In rollover incidents these air bags stay inflated for up to six seconds,” the company said. “Advanced glazing is designed to stay in the opening during the crash event to reduce further opportunity for full or partial ejections, providing a backing for the airbag or reaction surface.”

Leslie Shaver is a contributing editor to AGRR magazine.


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