Glass is one of the most critical safety and performance parts on modern cars. Windshields provide nearly one-third of the roof strength on the average car, and the front passenger air bags rely on windshield integrity for proper deployment. Plus, modern collision avoidance cameras need to see clearly and accurately through windshields. HVAC systems depend on UV filtering for efficient climate control operation, plus many cars and trucks now feature sound-deadening laminates to reduce wind and road noise.

Many people think of fascias strictly as cosmetic parts, but there are critical safety and performance issues related to their design. With more collision avoidance sensors now mounted to them, or aiming through them, fascias need to fit precisely for the systems to work accurately. As for performance, materials and construction are critical to ensure fascias fit properly, and that they do not warp or bind with body panels, causing them to rust or delaminate.

Of all the high-volume crash parts on a car today, few are more complex and critical to safety than today's headlamp assemblies. Exposed to the elements, they need to be robust and reliable so drivers can see and be seen at night. Alignment and proper fit affect safety and performance. Poor seals and leaky lamp assemblies are prone to condensation, corrosion and diminished output. Lens composites that yellow or fog also dramatically reduce light output.

Most people probably take side-view mirrors for granted, but today's mirrors are increasingly sophisticated. Aside from the convenience features of heaters, retractors and remote adjustment, self-dimming and multi-element reflective surfaces also affect safety and performance. For newer cars, crash avoidance and lane departure systems are also housed in the mirror assemblies, and are prone to failure due to inferior manufacture.