The correct answer is: no article.
The article "a" or "an" is used before a singular noun that refers to a general or unspecified thing. In this case, the accident is not a general or unspecified thing, but a specific accident that took place in a particular place. Therefore, the article "a" or "an" is not used.
The article "the" is used before a singular noun that refers to a specific or unique thing. In this case, the accident is not a specific or unique accident, but one of many accidents that could have taken place in the same place. Therefore, the article "the" is not used.
Without an article, the sentence is more concise and to the point. It also allows the reader to imagine what kind of accident took place, without being limited to a specific type of accident.
