Which of the following is NOT a common cause of vehicle fires?

The choice highlighting "Overheating brakes" as the answer is based on the fact that while brakes can indeed overheat and lead to various safety issues, they are not typically categorized as a common cause of vehicle fires. Overheating brakes can occur due to prolonged use, especially in mountainous driving scenarios, but the primary risks associated with brake overheating generally involve loss of braking efficiency rather than igniting a fire.

In contrast, spilled fuel poses a significant fire risk since fuel is highly flammable, and any ignition source can trigger a fire. The improper use of flares also constitutes a fire hazard as they are designed to produce flames and can ignite nearby combustibles. Similarly, accidents can lead to fires due to fuel leaks or ruptured gas lines, making them a well-documented cause of vehicle fires. Thus, overheating brakes, while a serious concern for vehicle safety, does not fall into the category of common fire causes in vehicles compared to the other options presented.