Table 4.

Results of the cumulative link mixed model.

Threshold Coefficients
Category	Estimate		S.D.		Z-value
Between property damage only and possible injury	−1.29		0.10		−12.42
Between possible injury and evident injury	2.52		0.11		23.61
Between evident injury and severe injury	4.67		0.11		42.17
Between severe injury and fatal	6.26		0.13		49.09
Independent Variables Coefficients
Category	Variable		Estimate		P-value
Fixed Effects
Human Factors
Demographic Profiles	Driver		2.65***		0.00
	Driver age		−0.01***		0.00
	Driver sex		0.56***		0.00
	Occupant age		0.01***		0.00
	Occupant sex		−0.22***		0.00
	The number of injured occupants		0.16***		0.00
Behavioral Factors	Alcohol use		1.07***		0.00
	Driver safety equipment use		−0.27***		0.00
	Improper driving		0.10.		0.05
	Unsafe speed		−0.10		0.35
	Occupant safety equipment use		−0.54***		0.00
Natural and Road Environment Factors
Temporal Factors	Summer		0.19***		0.00
	Weekday		0.06		0.13
	Nighttime		0.17***		0.00
Environmental Factors	Bad weather		−0.0008		0.99
	Dark/No streetlight		0.34***		0.00
	Slippery road surfaces		−0.16*		0.05
Location Characteristics	Intersection		−0.12*		0.01
	Ramp		0.34***		0.00
Collision Characteristics
Collision Characteristics	Head on		0.06		0.47
	Side swipe		−0.63***		0.00
	Rear end		−0.61***		0.00
Vehicle Characteristics
Vehicle Characteristics	Years of vehicle usage		0.02***		0.00
	Vehicle size		−0.43***		0.00
Interaction Effects
	Vehicle size: Unsafe speed		0.12**		0.001
Random Effects
Groups	Variable	Variance	S.D.	Intra-class Correlation
Driver sex: Driver age	Intercept	0.04	0.20	–	–	–
	Improper driving	0.06	0.25	−0.70	–	–
	Unsafe speed	0.08	0.29	−0.82	0.71	–
	Alcohol use	0.10	0.32	−0.49	0.52	0.43
Log-likelihood = −18,933.60	AIC = 37,945.20			n = 21,258

Significance codes: ‘***’ 0.001; ‘**’ 0.01; ‘*’ 0.05; ‘.’ 0.1