What is the worst car accident in history?

There's no single "worst" car accident in history because "worst" can be defined in many ways (highest death toll, most devastating long-term impact, most significant consequences for safety regulations, etc.). Different accidents might claim the "worst" title depending on the criteria used.

Several accidents are frequently cited for having extremely high death tolls, though precise numbers are often disputed due to the circumstances surrounding some of these events. For example, accidents involving large numbers of people crammed into vehicles or poorly maintained buses often result in extremely high casualty counts but may not be considered "car accidents" in the traditional sense. Furthermore, some historical accidents lack reliable documentation.

Therefore, there's no definitive answer to your question. It's important to understand that any high-casualty accident involving numerous vehicles or a large number of people represents a tragedy of immense proportions.