In what situation can windshield and back glasses be considered structural parts of a vehicle?

Windshield and back glasses can be considered structural parts of a vehicle primarily when they are set in urethane. This is because urethane provides a strong bond that contributes to the overall structural integrity of the vehicle. When windshields and rear windows are installed using urethane, they play a crucial role not just in providing visibility and protection but also in maintaining the vehicle's rigidity. This enhances the safety of the vehicle during a collision by helping to keep its shape and supporting the roof structure, which is essential in preventing roof collapse during rollover accidents.

The other options focus on characteristics of the glass, such as whether it is tempered or laminated, or how it is held in place (adhesive), but these aspects do not necessarily contribute to the structural role of the glass in the same way that urethane does. While tempered and laminated glass have their own benefits, they do not directly establish the glass as a critical structural component unless they are integrated in a way that uses urethane for mounting. Thus, the correct understanding is contingent upon recognizing the importance of urethane in enhancing the structural functionality of glass in vehicles.