| Name | Description | Range | Categorical value | |
| Site ID | Unique identifier for each site, used to account for repeated observations |
|
| |
| Volume | Annual average daily traffic | 400 to 8400 vpd |
| |
| Season | Season of the year | Categorical | Winter | |
| Spring | ||||
| Summer | ||||
| Fall | ||||
| Sign Type | Type of sign | Categorical | 0 | Control site |
| 1 | Speed display sign | |||
| 2 | Curve display sign | |||
| Tangent | Posted speed limit | 50 to 65 |
| |
| Advisory | Curve advisory speed limit | None and 15 to 50 |
| |
| Speed Diff | differential of posted and advisory speed | 0 to 40 mph |
| |
| Curve Type | Type of curve | Categorical | 0 | Isolated Curve |
| 1 | S-curve* | |||
| 2 | Several closely spaced* | |||
| Length | Length of treatment or control section; accounts for different section lengths | 0.40 to 2.0 miles |
| |
| Period | Installation period | Categorical | 0 | Control |
| 1 | Before installation of sign | |||
| 2 | Install quarter or quarter when signs were not functioning | |||
| 3 | After sign installation | |||
| Radius | Radius of curve | 138 to 5953 feet |
| |
| Year-2004 | Year after 2004, included to show trend over time | Categorical |
| |