Analysis of Injury Severity of Drivers Involved Different Types of Two-Vehicle Crashes Using Random-Parameters Logit Models with Heterogeneity in Means and Variances

Table 3

Model results of injury severity of drivers involved in different types of vehicle crashes.

Variables	Car-car crashes		Truck-truck crashes		Car-truck crashes
	CD model^a		TD model^a		CD model		TD model
	Coeff	t-stat	Coeff	t-stat	Coeff	t-stat	Coeff	t-stat
Constant	1.048	3.97	2.398	2.14	1.868	7.30	1.234	3.49
Random parameters
Age band of car driver (1 if 26–45 years, 0 otherwise)	0.471	2.46	—	—	—	—	—	—
Standard deviation values for 26–45 years car drivers (normally distributed)	0.328	3.54	—	—	—	—	—	—
Age band of truck driver (1 if 26–45 years, 0 otherwise)	—	—	0.569	2.51	—	—	0.152	1.14
Standard deviation values for 26–45 years truck drivers (normally distributed)	—	—	0.865	3.46	—	—	—	—
Heterogeneity in the mean of random parameter: male	0.598	4.12	—	—	—	—	—	—
Heterogeneity in the mean of random parameter: darkness—lights lit	—	—	−0.364	−1.67	—	—	—	—
Speed limit (1 if 30 mph, 0 otherwise)	−0.447	−3.56	−0.234	−1.75	−0.618	−3.95	−0.418	−4.15
Standard deviation values for the 30 mph speed limit (normally distributed)	0.185	6.07	0.271	8.80	—	—	0.789	14.36
Heterogeneity in the mean of random parameter: weekdays	—	—	—	—	—	—	0.476	2.54
Heterogeneity in the variance of random parameter: rural areas	—	—	—	—	—	—	1.094	7.03
Fixed parameters
Driver characteristics
Gender of car driver (1 if female, 0 otherwise)	0.444	3.52	—	—	0.410	2.43	—	—
Gender of truck driver (1 if male, 0 otherwise)	—	—	1.012	0.96	0.067	0.64	0.258	0.93
Age band of car driver (1 if 65 years above, 0 otherwise)	0.327	2.16	—	—	0.766	5.72	—	—
Age band of truck driver (1 if 65 years above, 0 otherwise)	—	—	0.601	1.31	—	—	0.093	0.31
Vehicle characteristics
Age of car vehicle (1 if 3–10 years, 0 otherwise)	—	—	—	—	−0.032	−0.24	—	—
Age of truck vehicle (1 if above ten years, 0 otherwise)	—	—	—	—	—	—	0.399	2.46
Car vehicle maneuver (1 if speeding, 0 otherwise)	0.959	2.69	—	—	0.228	1.90	0.407	1.01
Truck vehicle maneuver (1 if speeding, 0 otherwise)	—	—	0.013	0.02	—	—	—	—
Car vehicle maneuver (1 if turning, 0 otherwise)	0.345	2.83	—	—	—	—	—	—
Truck vehicle maneuver (1 if changing lane, 0 otherwise)	—	—	—	—	0.586	3.70	1.070	2.33
First point of impact (1 if front, 0 otherwise)	0.701	3.58	—	—	0.184	1.49	0.812	2.95
First point of impact (1 if offside, 0 otherwise)	0.571	2.34	−1.389	−4.28	0.789	3.51	—	—
Roadway characteristics
Road area type (1 if rural, 0 otherwise)	—	—	0.958	2.35	0.182	1.73	0.073	0.42
Road area type (1 if urban, 0 otherwise)	−0.314	−2.74	—	—	—	—	—	—
Road type (1 if dual carriageway, 0 otherwise)	0.273	2.16	—	—	0.237	1.65	—	—
Road type (1 if roundabout, 0 otherwise)	−0.645	−2.01
Road type (1 if junctions, 0 otherwise)	—	—	0.813	2.11	—	—	—	—
Environmental characteristics
Light conditions (1 if darkness-no lighting, 0 otherwise)	2.127	2.07	0.585	1.83	0.250	0.31	0.320	2.08
Light conditions (1 if darkness-lights lit, 0 otherwise)	0.503	3.22	—	—	—	—	—	—
Weather conditions (1 if fine, 0 otherwise)	−0.213	−1.97	—	—	—	—	—	—
Weather conditions (1 if raining, 0 otherwise)	—	—	0.742	2.33	0.981	2.40	—	—
Season (1 if summer, 0 otherwise)	0.253	2.66	—	—	—	—	—	—
Day of week (1 if weekdays, 0 otherwise)	—	—	0.071	0.28	—	—	0.521	2.62
Crash time (1 if off-peak time, 0 otherwise)	0.192	2.14	—	—	0.323	3.02	—	—
Goodness-of-fit measures
Number of observations	4992		681		2770		2770
Log-likelihood at convergence	−1885.2		−301.2		−1236.4		−844.5
McFadden R-squared	0.374		0.435		0.465		0.478
Akaike information criterion (AIC)	3814.4		628.4		2508.8		1730.9

^aTD: truck driver and CD: car driver.