Until recently, most of the glass used for side windows of automobiles was a single layer of tempered glass. The advantage of tempered glass is that it breaks into small pieces of particles rather than jagged pieces when broken. It is still the standard for most vehicles, but more and more manufacturers are turning to laminated glass, which has been used in windshields for decades because it resists breakage during impact.
This design is desirable in windshields because the federal government has found that a large number of drivers and passengers are being ejected from their vehicles in a car accident, thus changing vehicle design standards and forcing car manufacturers to use a sandwich design on the windshield. Try to reduce the chances of car accidents for drivers and passengers. Unfortunately, the side effect is that the resistance of the laminated glass is too great when it is necessary to break the side windows to escape the vehicle. However, this is a trade-off. The type of car accident on the road is more common than when people drive off the road into the water.
According to the American Automobile Association, the rear window of a typical car may still be made of tempered glass, so it is still possible to use a normal emergency escape hammer to break the glass escape.