Table 1: Response and Significant Independent Variable Descriptions.

Variable Name	Variable Description	Variable Type	Variable Categories
Severity (response)	Crash severity for barrier involved in crashes	Categorical	PDO Injury/Possible injury Fatality/ incapacitating
Road conditions	Indicator of roadway surface condition at the time of a barrier crash	Categorical	Dry (reference) Wet Snow Other (slush, sand) Ice
Speed compliance	Indicator of whether an estimated speed of an involved vehicle was within the range of posted speed limit	Categorical	Yes (reference) No
Negotiating Horizontal Curve	Indicator that whether a driver was negotiating a curve at the time of barrier crashes	Categorical	No (reference) Yes
Driver age	Indicator of the age of drivers involved in a barrier crash	Categorical	<35 years old (reference) >=35 years old
Driver gender	Indicator of the gender of a driver involved in barrier crashes	Categorical	Male Female
Driver conditions	Indicator of the driver condition at the time of a barrier crash	Categorical	Under normal conditions (Reference) Under non normal conditions
Type of impact	Indicator of the location of a vehicle that hit the barrier	Categorical	Other types of impact Other (Reference) Head-on
Alcohol citation record	Indicator whether a driver had an alcohol related citation in his record prior to involve in a barrier crash	Categorical	Did not have an alcohol citation (Reference) Had alcohol citation in the record
Driver citation record	Indicator whether a driver has any citation prior to being involved in a barrier crash	Categorical	Did not have any citation in his record (reference) Did have a citation in his record
Driver improper restraint	Indicator whether a driver restrained properly at the time of barrier crashes or not	Categorical	Restraint was used properly (reference) Restraint was not used properly