Table 3 Model results of mixed logit with heterogeneity in means and variance in single-vehicle crashes involving driving within the speed limit in the US, 2016–18.
Variable* | Parameter estimates | t-stat. | Marginal effects | ||
|---|---|---|---|---|---|
No injury | Minor injury | Severe injury | |||
Constant [SI] | -0.632 | -3.36 | |||
Random parameter (normally distributed) | |||||
Constant [MI] (Standard deviation of random parameters) | -2.828 (5.082) | -3.51 (4.62) | |||
Heterogeneity in mean of random parameter | |||||
Constant [MI]: Straight segment (1 if crashes occurred on straight segments, 0 otherwise) | -0.411 | -1.70 | |||
Heterogeneity in variance of random parameter | |||||
Constant [MI]: Clear weather indicator (1 if crashes occurred in the clear weather, 0 otherwise) | -0.461 | -2.76 | |||
Temporal characteristics | |||||
Time between 10 AM to 3:59 PM indicator (1 if crashes occurred between 10 AM to 3:59 PM, 0 otherwise) [MI] | 0.677 | 2.64 | -0.0082 | 0.0138 | -0.0056 |
4th quarter indicator (1 if crashes occurred between October to December, 0 otherwise) [NI] | 0.261 | 2.24 | 0.0101 | -0.0039 | -0.0062 |
Analysis Period 2017 indicator (1 if crashes occurred in 2017, 0 otherwise) [SI] | 0.208 | 1.85 | -0.0069 | -0.0021 | 0.0090 |
Ambient weather characteristics | |||||
Clear weather indicator (1 if crashes occurred in the clear weather, 0 otherwise) [MI] | 1.321 | 2.58 | -0.0472 | 0.0749 | -0.0278 |
Daylight condition indicator (1 if crashes occurred in daylight condition, 0 otherwise) [PDO] | -0.406 | -3.95 | -0.0293 | 0.0099 | 0.0194 |
Crash characteristics | |||||
Rollover indicator (1 if crashes were rollover, 0 otherwise) [MI] | 2.424 | 4.93 | -0.0248 | 0.0464 | -0.0216 |
Vehicle running off from the left of the roadway indicator (1 if a vehicle ran off the roadway from the left side of the roadway, 0 otherwise) [SI] | 0.531 | 5.06 | -0.0191 | -0.0050 | 0.0241 |
Tree indicator (1 if crashes involving with trees, 0 otherwise) [SI] | 1.116 | 7.99 | -0.0197 | -0.0047 | 0.0244 |
Vehicle characteristics | |||||
Motorcycle involvement indicator (1 if crashes involving motorcycle, 0 otherwise) [NI] | -3.510 | -4.79 | -0.0026 | 0.0006 | 0.0020 |
Displacement up to 2500 cc indicator (1 if crashes involved with the vehicles for displacement up to 2500 cc, otherwise) [MI] | -0.185 | -1.69 | -0.0255 | 0.0425 | -0.0170 |
Newer vehicle indicator (1 if crash involved with vehicles that were manufactured within 5 years from the year of collision, 0 otherwise) [MI] | 0.432 | 2.11 | -0.0091 | 0.0135 | -0.0043 |
Roadway characteristics | |||||
Two-way with positive median barrier indicator (1 if the crashes occurred in two-way roadway with positive median barrier, 0 otherwise) [SI] | 0.598 | 5.27 | -0.0172 | -0.0047 | 0.0219 |
Curved roadway indicator (1 if crashes occurred on curved roadways, 0 otherwise) [NI] | -0.561 | -4.24 | -0.0145 | 0.0047 | 0.0098 |
Dry surface indicator (1 if crashes occurred on dry surface, 0 otherwise) [NI] | -0.355 | -2.87 | -0.0407 | 0.0149 | 0.0258 |
Driver characteristics | |||||
Drives age up to 25 years (1 if drivers involved in crashes were up to 25 years old, 0 otherwise) [SI] | -0.185 | -1.69 | 0.0053 | 0.0014 | -0.0067 |
Reckless driving indicator (1 if crashes occurred due to reckless driving, 0 otherwise) [SI] | 0.384 | 2.80 | -0.0074 | -0.0023 | 0.0097 |
Driving under the influence (1 crashes occurred due to driving under influence, 0 otherwise) [MI] | 1.092 | 2.43 | -0.0026 | 0.0040 | -0.0013 |
Restraint usage indicator (1 if restraint used, otherwise) [NI] | 1.792 | 12.75 | 0.2241 | -0.0836 | -0.1405 |
Number of observations | 3450 | ||||
Log-likelihood at zero | -3790.212 | ||||
Log-likelihood at convergence | -3122.871 | ||||
ρ2 = 1 – LL(β)/LL(0) | 0.176 | ||||
