| Variable | Type | Unit | Description |
| CRASHRATE (EX-EN) | Endogenous | Million Vehicle Miles Traveled | Crash count per EX-EN segment taken over AADT and length in miles then multiplied by a million |
| CRASRATE (EN-EX) | Million Vehicle Miles Traveled | Crash count per EN-EX segment taken over AADT and length in miles then multiplied by a million | |
| TLANES | Exogenous | Number of Lanes | Number of through lanes |
| SHOULDER | Feet | Measurement taken from outside lane to edge of pavement | |
| MEDIAN | Feet | Measurement taken from insider lane to halfway of opposite direction inside lane edge of pavement | |
| AADT | Vehicles per Day | Average annual daily traffic | |
| GRADE | Percent | Average grade change for segment | |
| RADIUS | Feet | Curve radius | |
| LENGTH | Feet | Measurement taken from painted gore of ramp terminal to following painted gore | |
| AUX | No Unit - Indicator variable | Present of auxiliary lane |