|Factor||All fatal crashes||Single vehicle||Two vehicle||Multi-vehicles (three or more)|
|1||Traffic controls||Crash characteristics||Traffic controls||Road characteristics|
|2||Speed and route type||Traffic controls||Road characteristics||Speed and route type|
|3||Road characteristics||Speed and route type||Speed and route type||Road classification|
|4||Weather impacts||Weather impacts||Road classification||Traffic controls|
|5||Traffic flow||Road characteristics||Location of crash||Weather impacts|
|6||Crash characteristics||Traffic flow||Weather impacts||Drunk driving/light condition|
|7||Road classification||Road classification||Drunk driving/light condition||Persons|
|8||Persons||Persons||Persons||Location of crash|
NOTES: "Crash characteristic" relates to the crash's relation to the roadway and the first harmful event which occurred; "Persons" relates to the relationship between the number of persons involved in a fatal crash and fatality counts; "Drunk driving/light condition" is driven by the relationship between the FARS variables associated with drunk driving and the time of day.
SOURCE: U.S. Department of Transportation, National Highway Traffic Safety Administration, FARS Database, as of December 2009.