Table 2. Description of the independent and dependent variables.
| Variable types | Variables | levels | Code | Count | Percent |
|---|---|---|---|---|---|
| Traffic accident severity | NINP | 0 | 629 | 64.97% | |
| NIWP | 1 | 280 | 28.93% | ||
| WIWF | 2 | 59 | 6.10% | ||
| Environment conditions | Weather conditions | Sunny | 1 | 613 | 63.33% |
| Overcast | 2 | 132 | 13.64% | ||
| Light rain | 3 | 168 | 17.36 | ||
| Heavy rain | 4 | 55 | 5.68% | ||
| Lighting condition | Daytime | 1 | 715 | 73.86% | |
| Nighttime | 2 | 253 | 26.14% | ||
| Day type | Weekdays | 1 | 608 | 62.81% | |
| Weekends | 2 | 187 | 19.36% | ||
| Holidays | 3 | 173 | 17.87%% | ||
| Road geometry | Combine alignment | Straight + flat | 1 | 767 | 79.24% |
| Curve + flat | 2 | 187 | 19.32% | ||
| Straight + slope | 3 | 14 | 1.45% | ||
| Horizontal alignment | Straight | 1 | 318 | 32.85% | |
| Left curve | 2 | 359 | 37.09% | ||
| Right curve | 3 | 291 | 30.06% | ||
| Variable types | Variables | levels | Min | Max | Mean |
| Road geometry | Tangent length a (m) | Continuous variable | 245.75 | 2413.08 | 916.56 |
| Curve length b (m) | 514.38 | 3140.25 | 1044.47 | ||
| Curvature c (*0.001) | 0 | 2 | 0.5024 | ||
| Superelevation (%) | 0.13 | 8 | 2.35 | ||
| Road grade (%) | -3 | 3 | 0 | ||
| Slope length (m) | 320 | 2200 | 1068.10 | ||
| Traffic status | Traffic volume (1000 pcu/day) | 7.25 | 51.53 | 28.38 | |
| Percentage of trucks (%) | 1 | 37 | 19.81 | ||
a. 0 is not considered here, which represents that the horizontal segment is curve. b. 0 is not considered here, which represents that the horizontal segment is tangent. c. If without considering the tangent segment (curvature = 0), the minimum curvature is 0.167, and the mean is 0.7482.